Pregnancy puts between 25 and 40 pounds onto the front of a woman's body. It could pull her off-balance, but it doesn't. The new issue of the Journal Nature tells why. It has to do with the bones in the spine.
Walking while pregnant - it looks natural. According to the study, it is natural, but not simple. It involves a subtle change in a woman's backbone.
"The bones, which stack up on top of each other, referred to as the vertebral bodies, are shaped differently in a woman than in a man," Dr. Jeffrey Gross said.
It appears a woman's lower spine changes in pregnancy to allow her to carry a baby easily.
Normally, the center of gravity is right above the hip, because the hips and pelvis can support the whole body. When you pick up something heavy, it shift your weight forward, so you lean back to re-center the weight.
It seems a conscious process, says Jaclyn Ashear, who is 35 weeks pregnant.
"Your feet and your legs, it's like you're wobbling, you lean back as you walk forward to hold up your stomach," she said.
But a woman's spine repositions her center of gravity naturally, says the report. It's due to her lower vertebral bodies being wedge-shaped, not square, like a man's.
When a baby shifts a woman's center of gravity forward, the wedged-shaped bones allow the lower spine to curve forward. That moves her center back over the hips again.
But there's a price. Ask Alexandra Pena.
"You get a lot of back pain," she said.
"Usually during the visits, there's usually a little bit of comlaining about the back hurting," Dr. William Schweizer said. "Most patients brush it off as being part of normal pregnancy."
It is, because of pressure on the spine's facet joints.
"When the female bends backwards...more weight is put on the facet joints," Dr. Gross said. "And you can see the motion of these joints as I go forward and backward with the spine."
Dr. Gross says pregnant women can reduce this facet joint pressure and pain by avoiding high heels, by not standing in one place for too long and by wearing elastic supports made to reduce stress of the baby's weight on the lower back.
