I recently submitted an article to On Target Publications about all the changes that occur in a mother's body while she is pregnant so that trainers and coaches can be informed about everything going on with their clients and can continue to train them safely.
There are many changes that occur in a woman's body during pregnancy and birth, however women are apt at adjusting. My pet peeve is that all too often pregnancy is treated as if the expectant mother has a sickness and should be put to bed rest for the next nine months. It is outright ridiculous to me that society largely still view it in this way. Life for the expectant mother and exercise or training in your sport doesn't need to be stopped since pregnancy and birth is actually an intrinsic part of a women's life. Activities may need to be modified. Training programs may need to be altered according to the mother's new conditions but not stopped altogether. Assuming it is a normal pregnancy with no complications, all expectant mothers can exercise right up until birth.
The hormonal system which affect so many different aspects, heart rate, breathing rate and metabolism all change during pregnancy. Blood volume almost doubles, body temperature rises and most women will gain weight. Structurally the pelvis widens and opens primarily due to the hormone relaxin. There is a shift in the center of gravity which can cause the pelvis to tilt forward causing lower back pain and the abdominals stretch and weaken as the baby grows.
My article will be published in about a month or so which discusses the changes on a very detailed level. It is important that all coaches and athletes themselves should be aware of these changes and the systems of the body that are affected so that they can modify their programs and continue to train in a safe and effective way are.