Childbirth and the Obstetrical Dilemma

The human newborn's head fits the birth canal with millimetres to spare, and without care obstructed labour kills. But historical maternal deaths were mostly infection, toxaemia and bleeding, and the walking cost of a wider pelvis is near zero. The real trade-off is with the pelvic floor, which a designer would face too.

By AI (Claude Opus 5.5, reasoning effort unavailable) Draft:  September 2026

"This obstetrical dilemma was solved by delivery of the fetus at a much earlier stage of development." — Sherwood Washburn, Scientific American, 19601

"Mothers dying in childbirth is unheard of in chimpanzees, bonobos, gorillas, and all of our other primate cousins." — Nathan Lents, Human Errors, 20182

Summary

The complaint says a big-brained baby must squeeze through a pelvis kept narrow for walking, so human birth is uniquely dangerous and badly built.  The measurements support half of that.

  • The fit is tight. A newborn's head is about 12 by 9.5 cm. The opening at the top of the mother's pelvis is about 11.7 by 12.6 to 13 cm. The head has about a centimetre or less to spare along its length and must turn as it descends. In chimpanzees the fit is roomy.
  • Tight is not unique, and tight alone does not kill mothers. Japanese macaques have a fit as tight as the human one, and a 27-year record of 281 macaque births found no mother who died giving birth. Squirrel monkeys have lost up to half their young to a head stuck in the pelvis. No study was found that counts great-ape mothers dying in birth, so Lents's "unheard of" is unsourced, though no data contradict it.
  • Historical deaths were mostly not the pelvis. Before modern obstetrics about 1 birth in 50 to 1 birth in 200 killed the mother in England. Irvine Loudon's history puts sepsis at 33 to 50% of those deaths, toxaemia at about 20% and haemorrhage at 15 to 20%. A grossly contracted pelvis occurred in about 1 to 5 births per 1,000, mostly from childhood rickets, a disease of diet and sunlight. Today obstructed labour sits inside a WHO category that holds 9.6% of maternal deaths. Anatomy directly explains perhaps a tenth of historical deaths or less, with an unknown extra share through long labours that led to infection.
  • The textbook trade-off failed its test. Washburn's 1960 story said walking kept the pelvis narrow and birth was moved earlier. Measured walking cost does not rise with pelvic width, and a 2026 simulation from the dilemma's own defenders finds about 1% whole-body cost for a 20% wider pelvis. Human pregnancy is not short for a primate of our size.
  • A different trade-off has support. A wider canal leaves a larger pelvic floor to hold up the organs. A finite element model and a study of 31,115 UK Biobank scans both tie a larger canal to more pelvic floor trouble and a smaller canal to more obstructed labour. That trade-off would face any designer of a large-brained, upright animal.
  • The design replies are half right. Jerry Bergman at CMI is right that the pelvis serves several jobs and that rickets once caused much disproportion. "Rarely a problem" holds only with modern care. The Fall reading fits Genesis 3:16's multiplied pain, but no creationist source says what the pre-Fall pelvis looked like.
  • The lung-squeeze argument is unsupported. Babies born by caesarean without labour breathe; their small extra risk comes from missing labour, not the squeeze.

Verdict:  the fit is a real, measured constraint, and without care it is dangerous.  The critic's story about why it is tight has lost its main mechanism, and most historical deaths tracked care and nutrition, not bone.  The pelvic floor trade-off is the part a design argument must accept, and the Fall reading is weakest where it assumes a roomier original body without saying how.

Part 1: Who makes the argument

The term comes from Sherwood Washburn, an anthropologist at the University of California, in a 1960 Scientific American essay on tools.  He wrote that "In man adaptation to bipedal locomotion decreased the size of the bony birth-canal" while tool use selected for larger brains, and that "This obstetrical dilemma was solved by delivery of the fetus at a much earlier stage of development."11  That is three claims:  walking narrowed the canal, brains grew against it, and birth was moved earlier to cope.

Wilton Krogman had said the practical part in 1951:  "many of the obstetrical problems of Mrs. H. Sapiens are due to the combination of a narrower pelvis and a bigger head."3  Jerry Coyne made it an argument about design in 2009.  The pelvis "had to remain narrow to allow efficient bipedal (two-legged) walking," and "If you designed a human female, wouldn't you have rerouted the female reproductive tract so it exited through the lower abdomen instead of the pelvis?"44  Nathan Lents repeats Washburn's timing claim in 2018:  "The compromise is that fetal gestation is cut short, and human babies are born way before they are ready."2  He adds that maternal death is "unheard of" in other primates.2

Not every critic uses it.  A search of Olshansky, Carnes and Butler's whole-body redesign and of Richard Dawkins's The Greatest Show on Earth found no passage on the birth canal.5

The design claim, that a narrow pelvis is a poor way to deliver a big head, is tested in Parts 2 and 3.  The historical claim, that walking and brain growth pulled against each other, is tested in Part 4.

Part 2: The fit, in millimetres

A 2024 paper by Katharina Pink and colleagues gathers the standard measurements.6

Front to back Side to side
Human pelvic inlet (UK radiographs, 500 women; Swiss MRI, 781 women) 116.5–118.3 mm 126–130.3 mm
Human newborn head (UK, 106 boys and 106 girls) length 118.4–120.7 mm breadth 94.9–96.0 mm
Macaque pelvic inlet (CT, 4 females) 66.7–75.0 mm 56.8–64.4 mm
Macaque newborn head (377 newborns) length 67.0–70.1 mm breadth 52.2–54.6 mm

The human head is longer than the inlet is deep, so it enters sideways, with its length across the wider side-to-side diameter.  That leaves roughly 5 to 12 mm.  Lower down, at the level of the ischial spines, the pelvis is narrowest side to side, about 106 mm, and deepest front to back, about 123 mm.7  So the head has to turn a quarter-circle as it descends.8  The skull bones slide over each other, which buys a few millimetres more.9  The shoulders then have to turn too, and shoulder dystocia occurs in 1.4% of US births.7

The chimpanzee is different.  Its inlet is 136 mm front to back and 90 mm side to side.7  Natalie Laudicina and colleagues estimate a newborn Australopithecus sediba skull at about 89 by 73 mm and call it "only slightly larger than a neonatal chimpanzee cranium."7  The chimpanzee canal and head are both long front to back, and "the birth canal does not change shape or dimensions."7  At birth a human brain is at most 30% of adult mass, against 40% to 65% in great apes.10

Three things once called uniquely human are not.

  • Tight fits. Adolph Schultz's classic diagram showed "a tight fit in monkeys, gibbons and humans in contrast to relative spaciousness in great apes."9 The macaque figures above are as tight as the human ones.
  • Rotation. Radiographs of squirrel monkeys and baboons showed the head turning inside the canal.9 Video of three captive chimpanzee births showed babies emerging facing away from the mother, as human babies do, and turning after the head was out.11
  • Birth deaths. In squirrel monkeys, "stillbirths owing to cephalopelvic disproportion have been reported to be as high as 50% in one captive population."9

What does look distinctive is the combination.  Nicole Grunstra and ten co-authors, all defenders of the dilemma, write that "the human combination of a very tight fetopelvic fit, relatively immobile pelvic joints, and rotational birth appears to be unique among primates."10  Humans also seek help:  "routine assistance during birth is ubiquitous in and unique to humans."10  Of 296 cultures that mention attendance at birth, only 24 allow unattended delivery.9

Is maternal death "unheard of" in apes?  Lents gives no source.  The best data on a primate with a human-like fit come from Pink's team:  27 years of a monitored group of Japanese macaques, 281 births, and no mother died from birth.  Neonatal mortality was 8.9%.66  At a human-like 1% death rate, a count of zero in 281 births would happen by chance only 3.5% of the time.6  So tightness alone does not produce dead mothers.  Pink's team suggests the macaque pelvis and ligaments may give more, or its shape may make the passage smoother.6  A search found no count of maternal deaths at birth in wild or captive great apes.  Lents's claim fits the macaque data and has not been tested in apes.

Part 3: How many died, and of what

The rate.  Parish records from 13 English parishes give 10.5, 7.5 and 5.0 maternal deaths per 1,000 live births for 1700 to 1750, 1750 to 1800 and 1800 to 1850.12  Loudon's review of the English estimates puts the late seventeenth century higher, "around 150-60 per 10,000 births in the provinces and 210 in London," falling "to a level close to 50 by 1850."13  That is about 1 death in 48 to 1 in 200 births.  Pink's team quotes 0.8% for nineteenth-century Sweden and cites an estimate of about 1.5% for births with no effective care.6  Lents's "1 to 2 percent" floor matches seventeenth-century England, not 1750 to 1850.2  He reached it from Somalia's total maternal mortality in 2010, all causes counted.  For comparison, Finland recorded 3 maternal deaths per 100,000 live births in 2020, a rate about 170 to 350 times lower than England's in 1700 to 1850, with the same pelvis.6

The causes.  Loudon, a medical historian at Oxford, found that "the three most common causes of maternal mortality were sepsis (which accounted for between 33 per cent and 50 per cent of all maternal deaths), toxaemia (about 20 per cent of deaths), and haemorrhage (about 15-20 per cent of deaths)."13  William Farr's count for England and Wales in 1872 to 1876 put 55.5% of 23,051 maternal deaths down to puerperal fever alone.13  Geoffrey Chamberlain names "The Four Horsemen of Death in maternal mortality" as "puerperal pyrexia, haemorrhage, convulsions and illegal abortion."12  None of the four is a head stuck in the pelvis.

The pelvis.  Loudon gives obstructed labour a chapter.  Rickets "was by far the most common cause" of a small pelvis in the eighteenth and nineteenth centuries "and almost the only cause of really gross contraction."13  Even among the urban poor, "the incidence of gross contracted pelvis was quite low, ranging from about 1—5 in every 1,000."13  His conclusion:  "contracted pelvis probably made only a small contribution to maternal mortality."13  Removing every death that might have come from pelvic deformity does not remove the differences between countries.13  Loudon leaves one door open.  Mild contraction may have caused long labours and forceps deliveries that raised deaths from infection, and on that "no verdict can be given."13

Today.  Obstructed labour occurs in "3–6% of all births" and is thought to cause 8% of maternal deaths worldwide.14  Reported rates of cephalopelvic disproportion range from 1% to 8% by region.15  The WHO's analysis of 2003 to 2009 does not list obstructed labour separately.  It falls inside "all other direct causes," 9.6% of deaths, against 27.1% for haemorrhage, 14.0% for hypertensive disorders and 10.7% for sepsis.16

Babies.  In New York State in 1936 to 1938, before antibiotics were common, 27.8 babies per 1,000 were stillborn and 30.0 died in the first month.13  No source found here divides such deaths by cause for the pre-modern period.

How much is anatomy?  Obstructed labour is the pelvis's direct toll:  roughly a tenth of maternal deaths now, and by Loudon's account a smaller share in the past.  Two cautions pull opposite ways:  long labours feed infection, so some sepsis deaths began with a tight fit;  but the worst tight fits were made by rickets, a nutritional disease.  Grunstra's group, arguing for the dilemma, agrees that "fetopelvic disproportion affects only a small percentage of all births" when care is adequate, and that "other individual risk factors are equally or more important than anatomical limitations."1010  Loudon's own summary is that "the main determinant of maternal mortality was the overall standard of maternal care provided by birth attendants."17

Part 4: The trade-off story and its challengers

Washburn's story made three claims.  Each has now been tested.

Walking.  The trade-off assumed that a wider pelvis lengthens the lever the hip muscles work against, so walking costs more.  Holly Dunsworth and colleagues reviewed the gait studies in 2012:  "There is no evidence that female pelvic morphology affects locomotor cost."18  Anna Warrener's team measured it in 2015:  "pelvic width does not predict hip abductor mechanics or locomotor cost in either women or men."19  That study was small, and a null result is not proof of zero effect.  The confirmation comes from the other side.  In 2026 Ekaterina Stansfield and Philipp Mitteroecker, both co-authors of the pro-dilemma reply, simulated gait and found the hip muscles do work harder, but other muscles compensate, "leading to only minimal increases in whole-body metabolic cost (± 1% for ± 20% width change)."  Leg length matters 2.5 times more.20  One large study points the other way:  in UK Biobank, larger birth canals went with a slower self-reported walking pace, though its authors call the locomotor results "heavily mixed."2122

Timing.  Dunsworth's team argued that birth comes when the fetus's energy demand approaches the mother's sustained limit:  "By 9 mo, metabolic demands of the fetus threaten to push maternal energy requirements beyond 2.1× BMR."18  They also computed that passing a chimpanzee-stage brain of 640 cc would need about 3 cm more inlet, "within the range of pelvic dimensions seen in modern human females."18  Grunstra's group concedes that "humans have a gestation length expected for a primate of our body size."10  The UK Biobank team found no link between pelvic shape and gestation length, "contrary to the initial prediction by Washburn in 1960."21  So the claim that birth was moved earlier to fit the pelvis has not survived.

The pelvic floor.  Dunsworth herself suggested that wider pelves might raise "the likelihood of pelvic prolapse."18  Stansfield's 2021 finite element model varied the size of the pelvic floor and found that its sag "grew disproportionately fast with increasing radial size."23  The UK Biobank study, 31,115 scans, found that "narrower birth canals were associated with reduced pelvic floor disorder risk but increased obstructed labor risk."22  Grunstra's group calls pelvic size "only a minor risk factor" for these disorders, among many.10  The disorders are common:  a quarter to more than half of women in Western countries report at least one.23

Why does a tight fit persist?  Mitteroecker's "cliff-edge" model answers without any walking cost.  Fitness rises with a bigger baby until the baby cannot pass;  the best population average then leaves a small fraction over the edge.  "Weak directional selection for a large neonate, a narrow pelvic canal, or both is sufficient to account for the considerable incidence of fetopelvic disproportion."24  The same model predicts that caesarean sections have raised disproportion by 10 to 20% in two generations, though the authors call these figures "merely meant to represent orders of magnitudes."24  Barbara Fischer and Mitteroecker also found, in 99 museum pelves, that women with larger heads tend to have canals shaped for larger-headed babies, and short women have rounder inlets.14

Claim What it rests on
Wider pelvis costs walking energy Tested: not found (Warrener, data); about 1% per 20% width (Stansfield 2026, simulation); slower self-reported pace (Xu, data)
Gestation cut short to fit the pelvis Rejected: metabolic data (Dunsworth); no pelvis–gestation link (Xu, data)
Larger canal costs the pelvic floor Model (Stansfield 2021) plus association in 31,115 people (Xu, data)
Selection keeps some births over the edge Model only (Mitteroecker 2016); Grunstra: "built on a model, not on direct empirical observations"10
Caesareans are raising disproportion Model prediction, not measured (Mitteroecker 2016)

The defenders of the dilemma have kept the name and changed the mechanism.  The walking cost that Washburn and Coyne named has little support.  The constraint with support is the pelvic floor.

Part 5: The design replies, in their own words

What Genesis 3:16 says.  "Unto the woman he said, I will greatly multiply thy sorrow and thy conception; in sorrow thou shalt bring forth children."25  The same word "sorrow" describes Adam's labour in the next verse:  "in sorrow shalt thou eat of it all the days of thy life."25  The text claims multiplied pain in childbearing after the Fall.  It says nothing about the pelvis, the head, obstructed labour or death in childbirth.  Any anatomical reading is an inference.

AiG.  Physician Elizabeth Mitchell writes that "Eve was a real woman designed by God with the ability to enjoy easy labors producing healthy babies," and that "The human need for “help” in child delivery is not a product of evolution gone awry in the attempt to compensate for big brains and upright posture, but rather the result of the curse on an otherwise perfect creation."2626  She calls the pelvis "an ideal route of exit."26  Anatomist David Menton answers the design complaint that "all other mammals also deliver their live birth through their pelvic birth canal," and reads the extra pain through Genesis 3:16.27

CMI.  Jerry Bergman gives the fullest reply.  He states the trade-off:  "the female pelvis is designed to effectively serve several very different functions, including stable support for internal organs."28  He says "true cases of cephalopelvic disproportion are very rare today," and that in the past "due to illnesses such as rickets and polio, pelvic anomalies causing the birthing problems noted above were far more common than today."2828  He allows that "mutational load" since creation "may have had some adverse effects on childbirth."28  In a review of Lents he goes further:  "Actually, this is rarely a problem."29

Pricing the replies.

  • The trade-off answer is the strongest. Bergman's "stable support for internal organs" is the pelvic floor constraint that Stansfield and the UK Biobank team found. Secular work now says the canal is limited by a job the pelvis does, not by an evolutionary accident. That is what a design argument predicts.
  • The nutrition answer is right. Loudon confirms that rickets caused almost all gross contraction. Bergman's claim that most cases are "due to accidents" comes without a source or incidence data, however.28
  • "Rarely a problem" is true only with care. With midwives, antisepsis and surgery, disproportion is rare. Without them, Grunstra's group notes, maternal and neonatal death rates "increase dramatically," and obstructed labour still kills where care is poor.10 Bergman attributes "very rare" to the American Pregnancy Association, but both of his footnotes for it point to a parenting website.28
  • The Fall reading has no anatomy. Mitchell's easy-labouring Eve needs either a roomier canal or something else that made the same fit safe. A roomier canal meets the pelvic floor cost. The same fit, made safe, would need a mechanism, perhaps the looser joints Pink's team suggests for macaques. No creationist source found here proposes either. Bergman's appeal to mutation after creation is untested: no one has shown that pelvic or head dimensions have drifted.
  • Menton's "less than two inches wider" is unsourced and, if true, helps the critic.27

The lung-squeeze argument.  Eric's notes record a claim that "One purpose of the narrow birth canal is to sqeeze the amniotic fluid from the baby’s lungs," without which "breathing would be difficult if not impossible."  Its source is an anonymous blog comment.30  The primary data do not support it.  The liquid in a fetus's lungs is fetal lung liquid, and labour itself reduces it:  "During spontaneous labour there is a decrease in secretion of fetal lung liquid and an increase in its absorption."31  In rabbit pups born by caesarean, "94.8 +/- 1.4% of lung aeration occurred during inspiration."32  Human babies delivered by planned caesarean at 37 weeks have about four times the risk of breathing problems, falling with each later week, against 1.8% of all 34,458 Danish babies.3131  Labour helps the lungs.  A narrow canal is not required for breathing, and this argument should not be used.

Objections and responses

  1. "The deaths prove the design is bad whatever caused them." Only the deaths the design causes count against it. Infection after birth, eclampsia and most haemorrhage would kill a mother with a wider pelvis too. The pelvis's direct toll is obstructed labour, around a tenth of deaths.
  2. "Obstructed labour feeds sepsis and haemorrhage, so its share is understated." True, and Loudon says the question cannot be settled. But the same argument cuts the other way: the worst obstruction came from rickets, which is diet, not design. Both adjustments are unmeasured, so the article gives the direct share and flags the rest.
  3. "Coyne's abdominal exit would fix it." Coyne proposed it without any costing. An opening large enough for a 12 cm head through the abdominal wall is the problem that causes hernias, and women's walls are stronger precisely because nothing passes through them.33
  4. "Macaques prove the human pelvis is simply worse built." Macaques show that tight fits need not kill mothers. They walk on four legs, and in a quadruped the belly wall carries the organs "as in a hammock," while in humans they rest on the pelvic floor.9 That is the constraint Part 4 found.
  5. "The Fall explains it." Genesis 3:16 speaks of pain. Death and obstruction are not in the text, and a reading that adds them must say what the body was like before.

Issues and unanswered questions

  • No great-ape data. No count of maternal death at birth in wild or captive great apes was found. Lents may be right, and the design side cannot use the macaque result for apes.
  • The indirect share of anatomy is unknown, and so is the share of pre-modern stillbirths and newborn deaths caused by a tight fit. How many sepsis deaths began with a long labour is unmeasured, as Loudon says.
  • The pelvic floor constraint rests partly on a model. The UK Biobank association is large but observational, the walking pace is self-reported, and effect sizes were not taken from its figures. A 2026 Anatomical Record paper claiming empirical support for the cliff-edge model was found but not read.
  • The Fall reading has no reconstruction. No creationist source states the pre-Fall pelvis, head or birth mechanics. Until one does, the reply cannot be tested.
  • Bergman's sourcing. CMI's claims on the rarity and causes of disproportion rest on a parenting website. They agree in part with Loudon, but should not be cited for numbers.
  • Some critics' numbers have support after all. Lents's 1 to 2% matches late seventeenth-century England. The problem with his figure is its source, total modern mortality in Somalia, not its size.

Verdict

  • Real trade-off any upright, large-brained build faces: the size of the birth canal against the pelvic floor that must hold the organs. Two independent lines, a mechanical model and 31,115 scans, support it, and the design reply named it first in its own terms.
  • Share of historical deaths explained by anatomy: directly, about a tenth or less. Most mothers died of infection, toxaemia and bleeding, and the worst obstruction came from rickets. A fall of more than a hundredfold in maternal death with an unchanged pelvis shows that care, not bone, set the historical toll.
  • Where the critic is wrong: the walking cost Washburn and Coyne named is near zero at whole-body level, gestation is not cut short, and the abdominal exit is unpriced.
  • Where the design reply is weakest: "rarely a problem" said of birth without care; a Fall reading that implies a different pre-Fall body without describing it; Menton's unsourced two inches; and the lung-squeeze claim, which should be dropped.

Sources

  1. 1.

    Washburn, Sherwood L.  “Tools and human evolution.”  Scientific American 203(3):62–75.  Sep 1960.  Copyright.  Print-disabled archive.org copy read with bin/iapdsearch.py;  not stored.  Printed page = leaf − 7 by the item's scandata;  the title sits on leaf 70 = p. 63.  The OCR interleaves the columns, so quotations were reassembled from line fragments and only unbroken runs are quoted.  Mirror:  Archive.org

    1. 1a.

      Page 74:  “In man adaptation to bipedal locomotion decreased the size of the bony birth-canal”. ↩

    2. 1b.

      Page 74:  “This obstetrical dilemma was solved by delivery of the fetus at a much earlier stage of development.” ↩ ↩

  2. 2.

    Lents, Nathan H.  Human Errors: A Panorama of Our Glitches, from Pointless Bones to Broken Genes.  Houghton Mifflin Harcourt.  2018.  Copyright.  Print-disabled archive.org copy read with bin/iapdsearch.py;  not stored.  Printed page = leaf − 20 in the body, from the item's page map and the index entries "choking, 19" and "lithopedion, 116".  Mirror:  Archive.org

    1. 2a.

      Page 106:  “However, the size of the female pelvis limits how large the fetus’s head can grow while still in utero. If it grows too large, there is no way to get it out, and both baby and mother can perish. The compromise is that fetal gestation is cut short, and human babies are born way before they are ready.” ↩

    2. 2b.

      Page 110:  “In Somalia in 2010, there were 1,000 maternal deaths per 100,000 live births. That’s 1 percent of all births.”  “It seems that 1 to 2 percent is the lowest possible estimate when you consider that several countries (including Somalia) currently have that rate now.”  The OCR reads "/owest" for "lowest". ↩

    3. 2c.

      Page 111:  “Mothers dying in childbirth is unheard of in chimpanzees, bonobos, gorillas, and all of our other primate cousins.”  The print hyphenates "child- birth" across a line. ↩ ↩

  3. 3.

    Krogman, Wilton M.  “The Scars of Human Evolution.”  Scientific American 185(6):54–57.  Dec 1951.  Mirror:  Archive.org

    1. 3a.

      Page 56:  “there can be no doubt that many of the obstetrical problems of Mrs. H. Sapiens are due to the combination of a narrower pelvis and a bigger head in the species.” ↩

  4. 4.

    Coyne, Jerry A.  Why Evolution Is True.  Viking.  2009.  Copyright.  Print-disabled archive.org copy read with bin/iapdsearch.py;  not stored.  Leaf = page + 26, confirmed by the book's index entries "testes, 13, 84" and "childbirth, 85".  Mirror:  Archive.org

    1. 4a.

      Page 85:  “The problem is that as we evolved a big brain, the infant's head became very large relative to the opening of the pelvis, which had to remain narrow to allow efficient bipedal (two-legged) walking.” ↩

    2. 4b.

      Page 85:  “If you designed a human female, wouldn't you have rerouted the female reproductive tract so it exited through the lower abdomen instead of the pelvis? Imagine how much easier it would be to give birth!” ↩

  5. 5.

    Searches run 2026-09-27 with bin/iapdsearch.py on the print-disabled archive.org copies.  Olshansky, Carnes and Butler's article in the reader evolutionscienti0000unse, leaves 355–366:  no match for "birth".  Dawkins, The Greatest Show on Earth (2009), greatestshowonea00dawk:  no match for "birth canal".  Absence from a full-text search is not proof of absence from the book;  it shows the argument is not one these authors lean on. ↩

  6. 6.

    Pink, Katharina E. et al.  “No birth-associated maternal mortality in Japanese macaques (Macaca fuscata) despite giving birth to large-headed neonates.”  Proceedings of the National Academy of Sciences 121(42):e2316189121.  Oct 2024.  CC BY.  Read from the source-library copy.  Mirror:  PMC

    1. 6a.

      Table 1:  “Cephalopelvic dimensions”.  Values in mm.  Human obstetric conjugate mean 118.3 (UK radiographs, n = 500) and 116.5 (Switzerland MRI, n = 781);  transverse inlet 130.3 and 126.  Human newborn head length 120.7 (UK boys, n = 106) and 118.4 (girls, n = 106);  breadth 96.0 and 94.9.  Macaque inlet AP 66.7 to 75.0 and ML 56.8 to 64.4 (CT, n = 4);  newborn head length 70.1 (males, n = 214) and 67.0 (females, n = 163), breadth 54.6 and 52.2. ↩ ↩

    2. 6b.

      Section Significance:  “Japanese macaques show a human-like tight feto-pelvic fit. Based on 27 y of data from a continuously monitored semi-free-ranging group of Japanese macaques, we found no birth-associated maternal mortality in macaques, which differs from the situation in many human populations.” ↩

    3. 6c.

      Section Results:  “The neonatal mortality rate in this group was 8.9%.” ↩

    4. 6d.

      Section Results:  “The probabilities of obtaining zero maternal deaths by chance in the three tests are P = 0.1923, P = 0.0350, and P = 0.0028”.  Figure caption for the permutation tests at assumed rates of 0.5%, 1% and 2% on N = 281 births. ↩

    5. 6e.

      Section Abstract:  “ii) The macaque pelvis and connective tissue show greater flexibility during birth. iii) The interplay between macaque pelvic shape and birth dynamics is smoother and incurs fewer complications than in humans.” ↩

    6. 6f.

      Section introduction:  “In general, the frequency of human natural maternal mortality in settings with no availability of effective medical intervention, including well-trained midwives, is estimated at around 1.5% (24).”  “Comparable historical estimates based on a similar definition of maternal mortality as the WHO defines it range from 0.8% in Sweden (25) up to 1.57 to 2.1% in England (22, 26, 27).” ↩

    7. 6g.

      Section introduction:  “In 2020, human maternal mortality ranged from 3 maternal deaths per 100,000 live births in Finland to 1,223 maternal deaths per 100,000 live births in South Sudan”.  3 per 100,000 against England's 500 to 1,050 per 100,000 in 1700 to 1850 (Chamberlain Table 1) is a ratio of about 170 to 350. ↩

  7. 7.

    Laudicina, Natalie M. et al.  “Reconstructing birth in Australopithecus sediba.”  PLOS ONE 14(9):e0221871.  2019.  CC BY.  Read from the source-library copy.  Mirror:  PMC

    1. 7a.

      Table 1:  “Female pelvic dimensions for fossil hominins, modern humans, and chimpanzees.”  Values in mm.  Modern human (Tague and Lovejoy sample):  inlet AP 104.0, inlet ML 134.0, midplane AP 123.0, midplane ML 106.0 (n = 18), outlet AP 118.0, outlet ML 122.0.  Pan troglodytes:  inlet AP 136, inlet ML 90, midplane AP 117, midplane ML 71, outlet AP 122.4, outlet ML 105.0. ↩ ↩ ↩

    2. 7b.

      Section Introduction:  “Thus, the birth process in non-human apes is relatively simple compared to humans. The birth canal and the neonate’s head are elongated in the same plane (anterior-posterior) and the birth canal does not change shape or dimensions [2].” ↩

    3. 7c.

      Section Introduction:  “Birth complications due to shoulder obstruction, or shoulder dystocia, occur in 1.4% of the U.S. population [20], of which 24.9% result in fetal injury [21].” ↩

    4. 7d.

      Section Results:  “the A. sediba neonate would have a cranium with a biparietal breadth of ~73 mm and a frontal-occipital length of ~89 mm, only slightly larger than a neonatal chimpanzee cranium.” ↩

  8. 8.

    Rough arithmetic from two different samples, so the millimetres are indicative only.  Inlet:  head length 118.4–120.7 mm against a side-to-side inlet of 126–130.3 mm leaves 5 to 12 mm;  head breadth 94.9–96.0 mm against a front-to-back inlet of 116.5–118.3 mm leaves about 20 mm.6  Midplane (Tague and Lovejoy sample in Laudicina 2019):  side to side 106 mm, front to back 123 mm.7  A head 119 to 121 mm long cannot lie side to side in a 106 mm plane, so it turns to lie front to back, where 123 mm leaves 2 to 4 mm before moulding.  The macaque inlet (66.7–75.0 by 56.8–64.4 mm) against a head of 67.0–70.1 by 52.2–54.6 mm leaves between nothing and 8 mm on the long axis. ↩

  9. 9.

    Trevathan, Wenda.  “Primate pelvic anatomy and implications for birth.”  Philosophical Transactions of the Royal Society B 370:20140065.  2015.  Read from the source-library copy.  Mirror:  PMC

    1. 9a.

      Section 1:  “In a well-known diagram, Schultz [3] first depicted the relationship between neonatal head size and maternal birth canal as a series of rectangles (modified here as ovals) that showed a tight fit in monkeys, gibbons and humans in contrast to relative spaciousness in great apes (figure 1).” ↩

    2. 9b.

      Section 1:  “As an example, the small-bodied squirrel monkeys have one of the closest ratios among non-human primates; stillbirths owing to cephalopelvic disproportion have been reported to be as high as 50% in one captive population [5].” ↩

    3. 9c.

      Section 2:  “The cranial vault bones of human infants do not fuse until several years after birth and they can slide over each other (referred to as moulding), thus reducing the circumference of the fetal head temporarily to allow easier passage through the birth canal [15].” ↩

    4. 9d.

      Section 2:  “In quadrupeds, the weight of the abdominal organs (and the developing fetus in pregnancy) is distributed along the vertebral canal, where the abdominal wall acts to carry the contents, as in a hammock. In humans, abdominal contents (including the fetus during pregnancy) are carried by muscles of the pelvic floor”. ↩

    5. 9e.

      Section 4:  “Stoller's observations suggest that internal rotation during birth is not uniquely human, nor is it uniquely related to bipedalism.” ↩

    6. 9f.

      Section 6:  “Of the 296 cultures in which mention of attendance at birth is made, only 24 report that delivery may and does take place unattended [14].” ↩

  10. 10.

    Grunstra, Nicole D. S. et al.  “There is an obstetrical dilemma: Misconceptions about the evolution of human childbirth and pelvic form.”  American Journal of Biological Anthropology 181(4):535–544.  2023.  CC BY.  Read from the source-library copy.

    1. 10a.

      Section 2:  “Maternal and neonatal mortality and morbidity rates increase dramatically in the absence of midwifery and medical intervention, with obstructed labor and its sequelae resulting from fetopelvic disproportion being major contributors across different temporal, cultural and geographical contexts”. ↩

    2. 10b.

      Section 2:  “Actively assisted birth appears to be very rare in other primates; routine assistance during birth is ubiquitous in and unique to humans.” ↩

    3. 10c.

      Section 2:  “Clearly, most women are able to give birth vaginally when receiving adequate midwifery care; fetopelvic disproportion affects only a small percentage of all births.” ↩

    4. 10d.

      Section 2:  “(This is not in contradiction with the fact that, in modern obstetrics and midwifery, other individual risk factors are equally or more important than anatomical limitations.)” ↩

    5. 10e.

      Section 2:  “but the human combination of a very tight fetopelvic fit, relatively immobile pelvic joints, and rotational birth appears to be unique among primates.” ↩

    6. 10f.

      Section 3:  “Pelvic floor disorders have a complex etiology and pelvic dimensions are only a minor risk factor.” ↩

    7. 10g.

      Section 3:  “For instance, the risk of pelvic floor disorders increases roughly linearly with pelvic canal size. However, selection for a sufficiently large pelvic canal is truncational: if the birth canal is not large enough for the fetus, fitness drops sharply.”  “This argument is built on a model, not on direct empirical observations”. ↩

    8. 10h.

      Section 6:  “At birth, human newborns possess no more than 30% of adult brain mass, compared to 40%–65% in the great apes”.  “However, humans have a gestation length expected for a primate of our body size”. ↩ ↩

  11. 11.

    Hirata, Satoshi et al.  “Mechanism of birth in chimpanzees: humans are not unique among primates.”  Biology Letters 7(5):686–688.  2011.  Three captive births.  Read from the source-library copy.  Mirror:  PMC

    1. 11a.

      Section Abstract:  “In all three cases, the foetus emerged with an occiput anterior orientation, and the head and body rotated after the head had emerged. Therefore, these characteristics are not uniquely human.” ↩

  12. 12.

    Chamberlain, Geoffrey.  “British maternal mortality in the 19th and early 20th centuries.”  Journal of the Royal Society of Medicine 99(11):559–563.  2006.  Mirror:  PMC

    1. 12a.

      Table 1:  “Estimates of maternal mortality rates (MMR) from records of 13 English parishes in 50 year periods”.  MMR per 1,000 live births:  1700 to 1750, 10.5;  1750 to 1800, 7.5;  1800 to 1850, 5.0. ↩

    2. 12b.

      “The Four Horsemen of Death in maternal mortality were puerperal pyrexia, haemorrhage, convulsions and illegal abortion.” ↩

  13. 13.

    Loudon, Irvine.  Death in Childbirth: An International Study of Maternal Care and Maternal Mortality 1800–1950.  Clarendon Press.  1992.  Copyright.  Print-disabled archive.org copy read with bin/iapdsearch.py;  not stored.  Printed page = leaf − 28 by the item's scandata (leaf 159 = p. 131, leaf 475 = p. 447), confirmed by the index entry for nineteenth-century haemorrhage deaths at p. 97, whose paragraph and the chapter title "Obstetric Haemorrhage" sit on leaf 125.  Mirror:  Archive.org

    1. 13a.

      Page 43:  “the three most common causes of maternal mortality were sepsis (which accounted for between 33 per cent and 50 per cent of all maternal deaths), toxaemia (about 20 per cent of deaths), and haemorrhage (about 15-20 per cent of deaths).” ↩

    2. 13b.

      Page 97:  “In his review of maternal mortality for the five years 1872-6, William Farr noted that out of the total of 23,051 maternal deaths, 12,805 (55.5 per cent) were due to ‘metria’ (puerperal fever).” ↩

    3. 13c.

      Page 130:  “Rickets was not the only cause of a small or contracted pelvis, but it was by far the most common cause in the eighteenth and nineteenth centuries and almost the only cause of really gross contraction.” ↩

    4. 13d.

      Page 141:  “it seems that the incidence of gross contracted pelvis was quite low, ranging from about 1—5 in every 1,000”. ↩

    5. 13e.

      Page 142:  “This is the suggestion that minor degrees of contracted pelvis due to rickets led to long labours and sometimes to forceps deliveries in which the risk of maternal mortality was increased, chiefly by predisposition to puerperal fever.”  “no verdict can be given.” ↩

    6. 13f.

      Page 143:  “Although rickets was comparatively common and contracted pelvis from rickets certainly occurred, contracted pelvis probably made only a small contribution to maternal mortality.” ↩

    7. 13g.

      Page 160:  “Maternal mortality fell from a level of around 150-60 per 10,000 births in the provinces and 210 in London during the second half of the seventeenth century, to a level close to 50 by 1850.” ↩

    8. 13h.

      Page 447:  “Contracted pelvis, however, was not a major factor in international differences: if maternal deaths which may have been due to pelvic deformity— deaths following craniotomy, and deaths associated with Caesarean section, obstructed labour, or ruptured uterus (except where these deaths were linked to some other complication)—are removed from the lists of mortality, the international differences remain.” ↩

    9. 13i.

      Page 484, table 28.1:  “Neonatal and Stillbirth Rates according to whether the Mother Survived or Died, New York State (exclusive of New York City), 1936-1938”.  All deliveries:  stillbirth rate 27.8, neonatal mortality rate 30.0 per 1,000. ↩

  14. 14.

    Fischer, Barbara, and Philipp Mitteroecker.  “Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma.”  Proceedings of the National Academy of Sciences 112(18):5655–5660.  2015.  99 pelves (53 female) from the Hamann–Todd collection.  Read from the source-library copy.  Mirror:  PMC

    1. 14a.

      Section introduction:  “Obstructed labor occurs in 3–6% of all births and is thought to be globally responsible for 8% of all maternal deaths today (3–5).”  The 8% comes from Dolea and AbouZahr, Global Burden of Obstructed Labour in the Year 2000 (WHO, 2003), which was not obtained. ↩

    2. 14b.

      Section Abstract:  “Females with a large head, who are likely to give birth to neonates with a large head, possess birth canals that are shaped to better accommodate large-headed neonates. Short females with an increased risk of cephalopelvic mismatch possess a rounder inlet, which is beneficial for obstetrics.” ↩

  15. 15.

    Pavličev, Mihaela et al.  “Evolution of the human pelvis and obstructed labor: new explanations of an old obstetrical dilemma.”  American Journal of Obstetrics and Gynecology 222(1):3–16.  2020.  PMC author manuscript, read from the source-library copy.  Mirror:  PMC

    1. 15a.

      Section Cephalopelvic disproportion and obstructed labor:  “With this complexity in mind, reported CPD rates range from 1% to 8% of childbirths across different geographic regions11 (Source: WHO 2003).” ↩

  16. 16.

    Say, Lale et al.  “Global causes of maternal death: a WHO systematic analysis.”  Lancet Global Health 2(6):e323–e333.  2014.  Abstract read via Europe PMC.

    1. 16a.

      Section Abstract, Findings:  “Haemorrhage accounted for 27·1% (661 000, 19·9-36·2), hypertensive disorders 14·0% (343 000, 11·1-17·4), and sepsis 10·7% (261 000, 5·9-18·6) of maternal deaths. The rest of deaths were due to abortion (7·9% [193 000], 4·7-13·2), embolism (3·2% [78 000], 1·8-5·5), and all other direct causes of death (9·6% [235 000], 6·5-14·3).” ↩

  17. 17.

    Loudon, Irvine.  “Maternal mortality in the past and its relevance to developing countries today.”  American Journal of Clinical Nutrition 72(1):241S–246S.  2000.

    1. 17a.

      Section Abstract:  “It is suggested that the main determinant of maternal mortality was the overall standard of maternal care provided by birth attendants.” ↩

  18. 18.

    Dunsworth, Holly M. et al.  “Metabolic hypothesis for human altriciality.”  Proceedings of the National Academy of Sciences 109(38):15212–15216.  2012.  Mirror:  PMC

    1. 18a.

      Section Testing the Obstetrical Dilemma Hypothesis:  “In sum, biomechanical evidence fails to support the predictions of the OD hypothesis regarding locomotor cost. There is no evidence that female pelvic morphology affects locomotor cost, or that further neonatal brain expansion is evolutionarily constrained by pelvic mechanics.” ↩

    2. 18b.

      Section Testing the Obstetrical Dilemma Hypothesis:  “This suggests that birthing a neonate with a brain size 40% that of adults would require a 3-cm increase, on average, in the mother’s pelvic inlet to pass that larger fetus. A 3-cm increase is within the range of pelvic dimensions seen in modern human females”. ↩

    3. 18c.

      Section Metabolic Hypothesis for Gestation Length and Fetal Growth:  “By 9 mo, metabolic demands of the fetus threaten to push maternal energy requirements beyond 2.1× BMR. Extending gestation by even one month would likely require metabolic investment beyond the mother’s capacity.” ↩

    4. 18d.

      Section Discussion:  “Wider pelves may also increase the risk of injury, either through increasing the likelihood of pelvic prolapse ( 47 ) or by increasing mediolateral stresses on the knees and ankles ( 48 ).” ↩

  19. 19.

    Warrener, Anna G. et al.  “A Wider Pelvis Does Not Increase Locomotor Cost in Humans, with Implications for the Evolution of Childbirth.”  PLOS ONE 10(3):e0118903.  Mar 11, 2015.  CC BY.  Read from the source-library PDF.  15 adults in the metabolic experiment and 26 in the movement and MRI experiment.  Mirror:  PMC

    1. 19a.

      Page 1:  “The results show that pelvic width does not predict hip abductor mechanics or locomotor cost in either women or men, and that women and men are equally efficient at both walking and running.” ↩

  20. 20.

    Stansfield, Ekaterina et al.  “Did energy costs of walking limit the evolution of a larger human birth canal?”  Proceedings of the Royal Society B 293(2064):20252895.  Feb 2026.  Preprint doi 10.1101/2024.12.11.627886.  Abstract read via Europe PMC;  full text not read.  A musculoskeletal gait simulation, not a measurement on people.

    1. 20a.

      Section Abstract:  “Our results confirm that a wider pelvis substantially increases abductor muscle energy demands and activation (± 10% for ± 20% width change), consistent with predictions based on lever mechanics. However, during dynamic walking, these increased demands are offset by a redistribution of energy costs to other muscles, leading to only minimal increases in whole-body metabolic cost (± 1% for ± 20% width change). In contrast, lower limb length shows a 2.5-fold greater effect on metabolic cost than pelvic width.” ↩

  21. 21.

    Xu, Liaoyi et al.  “The genetic architecture and evolutionary consequences of the human pelvic form.”  bioRxiv.  May 3, 2024.  Preprint version 1 of the Science paper, CC BY, read from the source-library copy.  The published version may differ.

    1. 21a.

      Section Discussion:  “Our results on locomotion were heavily mixed, with larger birth canal phenotypes related to lower walking speed, reduced risk of back pain and knee OA, but increased risk of hip OA.” ↩

    2. 21b.

      Section Abstract:  “We found no association between any PPs and gestational duration, contrary to the initial prediction by Washburn in 1960.” ↩

  22. 22.

    Xu, Liaoyi et al.  “The genetic architecture of and evolutionary constraints on the human pelvic form.”  Science 388(6743):eadq1521.  2025.  Abstract read via Europe PMC.  UK Biobank participants aged 40 to 80;  walking pace self-reported.

    1. 22a.

      Section Abstract:  “By using deep learning on 31,115 dual-energy x-ray absorptiometry scans from UK Biobank, we identified 180 loci associated with seven highly heritable pelvic phenotypes.”  “Larger birth canals were linked to slower walking pace and reduced back pain but increased hip osteoarthritis risk, whereas narrower birth canals were associated with reduced pelvic floor disorder risk but increased obstructed labor risk.” ↩ ↩

  23. 23.

    Stansfield, Ekaterina et al.  “Biomechanical trade-offs in the pelvic floor constrain the evolution of the human birth canal.”  Proceedings of the National Academy of Sciences 118(16):e2022159118.  2021.  A finite element model.  Read from the source-library copy.  Mirror:  PMC

    1. 23a.

      Section Abstract:  “To test this “pelvic floor hypothesis,” we generated a finite element model of the human female pelvic floor and varied its radial size and thickness while keeping all else constant.”  “Deflection grew disproportionately fast with increasing radial size, and stresses and stretches also increased.” ↩

    2. 23b.

      Section introduction:  “In Western countries, a quarter to more than half of women report suffering from one or more pelvic floor disorders, with the reported prevalence of urinary incontinence ranging from 15 to 69% and of prolapse ranging from 6 to 41% (2–5).” ↩

  24. 24.

    Mitteroecker, Philipp et al.  “Cliff-edge model of obstetric selection in humans.”  Proceedings of the National Academy of Sciences 113(51):14680–14685.  2016.  A mathematical model with assumed inputs (3% prior incidence, heritability 0.5).  Read from the source-library copy.  Mirror:  PMC

    1. 24a.

      Section Abstract:  “Using a simple mathematical model, we show that weak directional selection for a large neonate, a narrow pelvic canal, or both is sufficient to account for the considerable incidence of fetopelvic disproportion. Based on this model, we predict that the regular use of Caesarean sections throughout the last decades has led to an evolutionary increase of fetopelvic disproportion rates by 10 to 20%.” ↩

    2. 24b.

      Section Materials and Methods:  “our predictions are merely meant to represent orders of magnitudes.” ↩

  25. 25.

    The King James Version of the Bible.  Project Gutenberg.  2024.  Public domain.  Text fetched and read 2026-09-27.

    1. 25a.

      Book Genesis, chapter 3, verse 16:  “Unto the woman he said, I will greatly multiply thy sorrow and thy conception; in sorrow thou shalt bring forth children; and thy desire shall be to thy husband, and he shall rule over thee.” ↩

    2. 25b.

      Book Genesis, chapter 3, verse 17:  “cursed is the ground for thy sake; in sorrow shalt thou eat of it all the days of thy life”. ↩

  26. 26.

    Mitchell, Elizabeth.  “The Evolution of Childbirth?”  Answers in Genesis.  Nov 15, 2006.  Mitchell is a physician.  Saved in the source library.

    1. 26a.

      Section opening:  “Eve was a real woman designed by God with the ability to enjoy easy labors producing healthy babies to do her part in filling the earth.” ↩

    2. 26b.

      Section opening:  “The human need for “help” in child delivery is not a product of evolution gone awry in the attempt to compensate for big brains and upright posture, but rather the result of the curse on an otherwise perfect creation.” ↩

    3. 26c.

      Section Evolution and the Female Body:  “The anatomy of the pelvis, instead of making human labor difficult, provides an ideal route of exit.” ↩

  27. 27.

    Ham, Ken.  “Is the Human Body a Bad Design?”  Answers in Genesis.  Jun 4, 2020.  Most of the text is anatomist David Menton's reply, quoted by Ham.

    1. 27a.

      Section The human pelvic birth canal:  “But all other mammals also deliver their live birth through their pelvic birth canal. It is true that humans seem to endure more pain in the same process than do most animals. Genesis 3:16 explains this, that the greater pain in the human birth process is a result of sin”. ↩

    2. 27b.

      Section The human pelvic birth canal:  “it is estimated that the human pelvis would only need to be less than two inches wider to more comfortably accommodate the relatively large head of the human newborn.” ↩

  28. 28.

    Bergman, Jerry.  “The poor design claim of the human birth canal examined.”  Journal of Creation 33(1).  2019.  Web version dated 7 December 2024, saved in the source library.  The article has no subheadings;  locators are paragraph positions.

    1. 28a.

      Paragraph the paragraph defining cephalopelvic disproportion:  “According to the American Pregnancy Association, true cases of cephalopelvic disproportion are very rare today.”  The sentence carries Bergman's note 31, which is M. Pyanov, "Small pelvis? Big baby? Here’s the truth about CPD", bellybelly.com.au, June 2018.  His second "very rare" sentence carries note 36, "Pyanov, ref. 31, pp. 1–3." ↩ ↩

    2. 28b.

      Paragraph the paragraph after the US maternal death figures:  “The majority of cephalopelvic disproportion cases are due to accidents, such as a pelvic fracture from a sports or traffic accident, or birth defects that damage the pelvis, poor nutrition that results in rickets, illnesses such as polio that lead to pelvic anomalies, and hormone deficiencies such as abnormally low levels of oxytocin.”  No footnote follows this sentence. ↩

    3. 28c.

      Paragraph the paragraph on failure to progress:  “In the past, due to illnesses such as rickets and polio, pelvic anomalies causing the birthing problems noted above were far more common than today.” ↩

    4. 28d.

      Paragraph the third paragraph from the end:  “Furthermore, the female pelvis is designed to effectively serve several very different functions, including stable support for internal organs.” ↩

    5. 28e.

      Paragraph the second paragraph from the end:  “Conversely, the mutational load that has accumulated in humans in the past 6,000 years since creation may have had some adverse effects on childbirth, causing the data to imperfectly reflect the original design which God declared “very good”.” ↩

  29. 29.

    Bergman, Jerry.  “A book about human errors that don’t exist.”  Journal of Creation 33(2):33–37.  Aug 2019.

    1. 29a.

      Section The claimed birthing problem:  “Actually, this is rarely a problem. The birthing system’s design ensures that almost all healthy mothers birth without problems except the birthing pain mentioned in Genesis due to Eve’s sin.” ↩

  30. 30.

    Eric's research note /home/share/notes/eric/research/biology/bad design.md, section "Narrow birth canal", quoting a reader comment at http://www.uncommondescent.com/intelligent-design/from-salon-again-four-reasons-why-id-supposedly-falls-flat/#comment-510949.  The comment gives no source.  A search for a primary source measuring a mechanical squeeze as necessary for breathing found none;  the sources in this section measure what does clear the lungs. ↩

  31. 31.

    Hansen, Anne Kirkeby et al.  “Risk of respiratory morbidity in term infants delivered by elective caesarean section: cohort study.”  BMJ 336(7635):85–87.  2008.  34,458 births, Aarhus, Denmark, 1998 to 2006.  Read from the source-library copy.  Mirror:  PMC

    1. 31a.

      Section Abstract, Results:  “Compared with newborns intended for vaginal delivery, an increased risk of respiratory morbidity was found for infants delivered by elective caesarean section at 37 weeks’ gestation (odds ratio 3.9, 95% confidence interval 2.4 to 6.5), 38 weeks’ gestation (3.0, 2.1 to 4.3), and 39 weeks’ gestation (1.9, 1.2 to 3.0).” ↩

    2. 31b.

      Section Results:  “The frequency of respiratory morbidity was 1.8% (n=604), with 0.2% (n=64) having serious respiratory morbidity”. ↩

    3. 31c.

      Section Discussion:  “During spontaneous labour there is a decrease in secretion of fetal lung liquid and an increase in its absorption and the release of surfactant is stimulated. This may be mediated by a raised level of catecholamines in the fetus in response to rupture of membranes and labour.” ↩

  32. 32.

    Siew, Melissa L. et al.  “Inspiration regulates the rate and temporal pattern of lung liquid clearance and lung aeration at birth.”  Journal of Applied Physiology 106(6):1888–1895.  2009.  Abstract read via Europe PMC.  Rabbit pups, not human babies.

    1. 32a.

      Section Abstract:  “Near-term rabbit pups (n = 26) were delivered by cesarean section”.  “As a result, 94.8 +/- 1.4% of lung aeration occurred during inspiration over multiple breaths.”  “We conclude that lung aeration is predominantly achieved by inspiratory efforts”. ↩

  33. 33.

    Shubin, Neil.  Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body.  Pantheon Books.  2008.  Copyright.  Print-disabled archive.org copy read with bin/iapdsearch.py by the parent article;  printed page = leaf − 14.  Mirror:  Archive.org

    1. 33a.

      Page 196:  “Because females do not have a giant tube running through it, their abdominal wall is much stronger than a man’s. This is a good thing when you think of the enormous stresses that female body walls go through during pregnancy and childbirth. A tube through the body wall just wouldn’t do.” ↩