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(Ivanhoe Newswire) – Changes in a woman’s spine may explain how her body can compensate for the strain and weight of being pregnant.

A new study from Harvard University and the University of Texas at Austin finds women’s lower spines evolved to be more flexible and supportive than men’s to increase comfort and mobility during pregnancy and to be able to carry a baby for nine months while standing on two feet.

Researchers studied 19 pregnant women between the ages of 20 and 40. They found when the women are naturally standing they lean back which increases their lordosis – the inward curvature of the spine – by as much as 60 percent by the end of their term. By doing this pregnant women keep a stable center of gravity above their hips.

Results also show a female’s lordosis extends across three vertebrae while a man’s only curves across two. And the female joints are relatively larger and flare out further down the spine than a male’s. The combination makes a woman better able to extend the spine, so she can lean back, realign the body’s center of gravity, and safely maintain a more stable position.

The ability of women to better carry a baby to term while standing on two feet seems to have evolved at least two million years ago - the researchers studied two hominin fossils that were about two million years old.

“Early human women lived very strenuous, active lives, and pregnant females were forced to cope with the discomfort of childbearing while foraging for food and escaping from predators,” co-author Daniel Lieberman, University of Texas at Austin, was quoted as saying. “This evolution of the lower back helped early woman to remain more mobile during pregnancy, which would have been essential to survival, and appears to have been favored by natural selection.”

This article was reported by Ivanhoe.com, which offers Medical Alerts by e-mail every day of the week. To subscribe, click on: http://www.ivanhoe.com/newsalert/.

SOURCE: Nature, 2007

This entry was posted on Friday, December 14th, 2007 at 2:12 pm and is filed under Medical News. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.