Question: what happens in the belly?

Kate Clancy answered on 13 Jun 2011:

If by belly you mean uterus, or womb, you asked the right person! 🙂

Before you start getting your periods very little is happening in your belly. But when your body has grown enough that it seems to make sense to start allocating energy to reproduction, and not just getting taller, it’s like the train changes tracks. So then you are on the reproduction track and everything wakes up.

Over the course of a menstrual cycle, when they start becoming somewhat regular (which takes 5-12 years after your very first one), you are growing a lush lining to your uterus. In the first half of the cycle you just grow the lining to be thick, and in the second half of the cycle you are making it lush: imagine lots of nooks and crannies for nutrients. If there is no baby, that lining comes out and you have your period. If there is a baby, more cool stuff happens…

Pregnancy is divided into three trimesters. In the first trimester, you are mostly just growing your placenta, which is a big organ — several pounds — that is often called the tree of life. This is the link between a mother and her fetus: the placenta protects the fetus from too many hormones from the mom, and it regulates the amount of nutrients the fetus gets. During the first trimester the fetus isn’t much more than a bean, and while that placenta is getting organized the lining of your uterus uses all the nutrients in those nooks and crannies to help feed the fetus.

In the second trimester, the placenta is fully established and the baby really gets growing! Many women enjoy the second trimester the most, because they are getting used to being pregnant and growing the fetus seems less exhausting than growing the placenta. (At least, that’s my take after having one myself a few years ago!)

The third trimester is when the baby is really getting big, and towards the end a few interesting things are happening in your belly. First, the placenta is getting tired. It is reaching its limit of how long it can continue to help the fetus. Second, the mother is getting tired. She may be reaching the limit of how much nutrition she can give the baby while it’s inside her. Inside the body may seem like the safest place for a baby, but once it starts getting big it can’t get enough calories to survive while inside.

So… at the very end of the pregnancy, when the mother is actually losing weight even as the fetus is gaining, finally the fetus’s weight gain slows and it feels stress. This is GOOD stress, because that means it’s going to tell the placenta, tell my mommy to get me out of here! And that is how labor starts. Then hormones make the muscles in your belly contract in order to help the cervix get big enough to push the baby through.

The last thing I’ll say about this is that, no matter how interesting the belly is, what then happens during breastfeeding is equally cool. Pregnant women only need an extra 200-300 calories a day, but breastfeeding women need 400-600! That’s twice as much! And that’s because the fat and energy of breastmilk is a lot harder to make than the incremental growth of the baby. And that’s why it is so often easier to lose weight after having a baby if you breastfeed exclusively.

Sorry this is such a long answer, you just happened to hit on my specialty. 😉