Large headed women found to have pelvis shape to allow for delivery of large headed babies

April 21, 2015 by Bob Yirka report
The skull of a newborn must fit through the female pelvis at birth -- it has to be as big as the diameter of the birth canal. Credit: Copyright: Magdalena Fischer

(MedicalXpress)—A pair of researchers, one with the University of Oslo, in Norway, the other with the University of Vienna in Austria, has found that women with large heads tend to have birth canals that are shaped differently on average to accommodate what will likely be babies being born with larger heads. In their paper published in Proceedings of the National Academy of Sciences, Barbara Fischer and Philipp Mitteroecker describe how they analyzed multiple human skeletons and noticed a trend—women with large heads had slightly differently shaped birth canals.

Big heads do not always mean large egos—some people actually have heads that are physically larger than average, which causes some other people, mostly women, to wonder about how things went when that baby was being delivered—a large , it would seem, would have more difficulty passing through the pelvic bones that make up the birth canal, causing the mother more distress than for mothers delivering smaller headed babies. But nature has found a way to help, it appears, as the two researchers discovered.

As part of a larger study to try to understand why it is that female human beings have on average narrow hips and thus a small , relative to baby size, the researchers examined 99 , looking for clues. While they were not able to answer the question of why the female pelvis has not grown larger to accommodate the larger head that has evolved to hold our growing brains, they did spot a trend—they noticed that women with larger heads tended to have a that was structured slightly differently that would help in allowing passage of a baby with a larger than average head. A nice adaptation, they note, for such women, but it does not explain why the female pelvis has not evolved along with the brain—thanks to modern medicine, many more women today survive childbirth than at any other time in history, but if the pelvis had widened over the past generations, than women giving birth would not be at so much risk in the first place.

With the use of 3-D data, the authors identified a relationship between the shape of the pelvis, the body size and head circumference. Credit: Copyright: PNAS

The researchers note that the pelvis actually serves two purposes for , reproduction and locomotion—they suggest that nature has preserved the smaller pelvis because of some locomotive advantage, though no one has been able to show what that advantage might be.

Explore further: Research refutes long-held theory: Mother's metabolism, not birth canal size, limits gestation

More information: Covariation between human pelvis shape, stature, and head size alleviates the obstetric dilemma, Barbara Fischer, PNAS, DOI: 10.1073/pnas.1420325112

Compared with other primates, childbirth is remarkably difficult in humans because the head of a human neonate is large relative to the birth-relevant dimensions of the maternal pelvis. It seems puzzling that females have not evolved wider pelvises despite the high maternal mortality and morbidity risk connected to childbirth. Despite this seeming lack of change in average pelvic morphology, we show that humans have evolved a complex link between pelvis shape, stature, and head circumference that was not recognized before. The identified covariance patterns contribute to ameliorate the "obstetric dilemma." 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. We suggest that these covariances have evolved by the strong correlational selection resulting from childbirth. Although males are not subject to obstetric selection, they also show part of these association patterns, indicating a genetic–developmental origin of integration.

Related Stories

Research refutes long-held theory: Mother's metabolism, not birth canal size, limits gestation

August 27, 2012
New research by a University of Rhode Island professor suggests that the length of human pregnancy is limited primarily by a mother's metabolism, not the size of the birth canal. The research, published in the Proceedings ...

Women born early at greater risk of delivering preemies, study suggests

April 10, 2015
(HealthDay)—Women who were born prematurely may be more likely to deliver their own babies early, a new study suggests.

Virtual childbirth simulator improves safety of high-risk deliveries

November 29, 2011
Newly developed computer software combined with magnetic resonance imaging (MRI) of a fetus may help physicians better assess a woman's potential for a difficult childbirth. Results of a study using the new software were ...

Pelvic widening continues throughout a person's lifetime, study

May 25, 2011
By the age of 20, most people have reached skeletal maturity and do not grow any taller. Until recently it was assumed that skeletal enlargement elsewhere in the body also stopped by age 20.

Recommended for you

Hope for couples suffering IVF miscarriage

September 20, 2017
Women who miscarry during their first full round of IVF are more likely to have a baby after further treatment than women who don't get pregnant at all.

Does mother's mental health affect pregnancy?

September 13, 2017
(HealthDay)—Three common mental health disorders—depression, panic disorder and generalized anxiety disorder—pose no serious threat to pregnant women or the health of their babies, a new study finds.

Preeclampsia may boost heart disease risk by altering blood vessels

September 12, 2017
Preeclampsia may permanently change the blood vessels of women who experience the condition during pregnancy, boosting their lifelong risk for cardiovascular disease, according to Penn State researchers.

Discovery of genes linked to preterm birth in landmark study

September 6, 2017
A massive DNA analysis of pregnant women has identified six gene regions that influence the length of pregnancy and the timing of birth. The findings, published today in the New England Journal of Medicine, may lead to new ...

Older wombs linked to complications in pregnant mice

September 5, 2017
Deciding to start a family later in life could be about more than just the age of your eggs. A new study in mice suggests the age of a mother's womb may also have a part to play. This work, led by Dr Myriam Hemberger at the ...

Study suggests simple way to predict preterm births

September 4, 2017
Up to 18 percent of babies born worldwide arrive before they are full-term, defined as 37 weeks of gestation. About 1 million of those babies do not survive, and those who do can face developmental problems such as impaired ...


Adjust slider to filter visible comments by rank

Display comments: newest first

5 / 5 (1) Apr 21, 2015
All our child care support and keeping people alive who would otherwise have died in the process (All good as far as anyone is concerned) are probably stunting general evolution of traits that would help both mother and child survive childbirth, because we have behaviorally evolved to cope with it instead. Otherwise all of those people who were likely to die in child birth would have, and their kids would have never bred, etc.
not rated yet Apr 22, 2015
With intelligent beings technology may be more successful than random evolution, which is why it probably appeared.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.