Physical Changes in the Third Trimester

“The (physical) changes for the mom and baby during the third trimester are all getting things ready for the baby to be born and to live independently and to nurse to breastfeed. So a lot of the changes in the third trimester are related to that. The mom’s breast will start to develop in a way that she’ll be able to make milk soon after the baby’s born.”

Changes in Baby

“The baby is mainly putting on weight and there’s lung development and brain development in the last trimester, but the baby’s fully formed. It looks like a little baby, just tinier, and will primarily be putting on weight in the last trimester.

Cardiovascular Changes

“Also, mom’s blood volume is going to expand again. So she may notice some swelling occasional, particularly after activity. But that’s to make sure she has a good reserve of blood for the birth.”

Musculoskeletal Changes

“So another thing a lot of moms will notice in the third trimester, particularly in the last month, is that as the baby gets bigger and bigger. Her center of gravity gets thrown off. She may have some back pain or feel loose joints. And that’s from a hormone called relaxin that helps all the joints in the mom’s body, particularly her pelvis expand and relax so that they’re mobile for the delivery. And that’s very helpful. So that’s very normal to feel those kinds of loose joints and the way you walk may change. People talk about waddling as they get closer to birth. That’s all from everything loosening up. This is a good thing. It’s what your body needs to do to be ready for birth.”