From pelvic bone separation (eek!) to the real reason you're waddling, we're betting you didn't know these six things about your pregnant body!
pregnant body
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With all the information now available to us about pregnancy, labor, and delivery, it can be easy to feel that we know all there is to know.

But the truth is, there is still a lot of mystery surrounding pregnancy and birth. For instance, did you know that we still don't know what exactly causes labor to start?

Luckily, not all things about pregnancy need to remain a mystery. Discover six wow-inspiring ways your body changes during pregnancy.

1. Your uterus is one tough cookie. The force inside a woman's uterus from pushing with a contraction translates to 397 pounds of pressure per square foot, or 2.8 pounds of pressure per square inch on her baby's head.

2. What was that noise? It's painful yet true -- the first time a woman delivers a child, her pelvic bone will actually separate in the middle. "The cartilage stretches at the middle of the pubic bone," explains Nina N. Hinting, M.D., a physician in the Obstetrics and Gynecology Division at Sinai Hospital of Baltimore. "The bone doesn't break, but it never really goes back together either -- it's not made to go back together."

3. You can get pregnant when you're already pregnant. Pregnancy sex is supposed to be care- (and contraceptive-) free, but on rare occasions, women have gotten pregnant twice. It happened to a woman in Arkansas, who carried two children with two different due dates.

4. One size does not fit all. There are actually four different shapes that a woman's pelvis can take. Unfortunately, only one is best for accommodating a baby's head during childbirth -- the gynecoid. Fortunately, that shape happens to be the most common.

5. That line was actually always there. You know that dark line (linea nigrea, or black line) that suddenly appears straight down the middle of your stomach during pregnancy? It's not a mystery how it got there. "That line was actually always there," Dr. Hinting explains. "But pregnancy hormones change the pigmentation to make it show more."

6. That waddle is not your fault. Feeling self-conscious about your duck walk? It may not have anything to do with your size or weight. "The waddle is actually due to the fact that the joints become more relaxed and the center of gravity changes," Dr. Hinting says. "Pregnant women walk a little bit wider -- that's why you waddle."

Mysteries -- solved!

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