When it comes to pregnancy, doctors say it's no time to become a couch potato.
In fact, the American College of Obstetrics and Gynecology says working out is just as important as ever when a woman is carrying a baby. Exercise helps a woman look and feel better at a time when her body is going through major changes.
One woman took that advice and swam with it.
Stephanie Wolmer's fourth child is due in about 12 weeks. A life-long athlete, Stephanie, 43, swims at least five times a week at her neighborhood pool. Her workouts aren't as intense as they were before pregnancy, but she still feels they are helpful.
But not all women are as fit as Wolmer, who is a veteran marathon runner, in addition to her swimming strengths. So how should other pregnant women go about exercising?
During pregnancy, a woman wants to do everything she can to ensure safety and health both for herself and for the developing baby, says CBS News health contributor and sports medicine specialist Dr. Jordan Metzl.
First and most importantly, Metzl says, it is important to talk with your doctor about working out. Talk about how often you would like to exercise and what activities you would like to take part in.
If it has been a while since you last exercised, it's a good idea to start slowly. Begin with as little as 5 minutes a day and add 5 more minutes a week until the exercise time gets up to 30 minutes a day.
Always begin with a 5-10-minute warm-up, which should include gentle stretching, Metzl says, and end with a 5-10-minute cool-down, which allows the heart rate to return to normal.
The best activities for a pregnant woman are swimming, brisk walking, and stationary biking. It's best to avoid high-stress activities, excessive exercise, and anything that will restrict blood flow to the developing baby.
Avoid any sport that is very jarring to the body, including high-impact aerobics and heavy-duty running. Also, after 20 weeks, a pregnant woman should avoid any exercise that requires her to lie flat on her back, because it may be more difficult for blood to circulate to the fetus as a result.
Other changes that take place in the body during pregnancy may affect the ability to exercise, Metzl says.
For instance, the hormones produced during pregnancy cause the ligaments that support the joints to become more relaxed. This makes the joints more mobile and more at risk for injury. This is why it's advisable to avoid high-impact motions and full-extension bicep curls.
Also, during pregnancy, a woman is carrying extra weight in the front of her body. This shifts the center of gravity and places stress on joints and muscles, especially those in the pelvis and lower back. The weight also causes low back pain. All of this contributes to making a woman unstable and more likely to lose her balance.
It's also important to be aware of body temperature. Pregnant women tend to tire more easily, and their body temperature gos up more quickly. It is very important that a pregnant woman not exercise to the point that she is sweating profusely and feels faint.
The "talk test" can determine whether or not a pregnant woman is working out too hard, Metzl says. If she's not able to talk easily, then she should quit.
It is also very important that a pregnant woman monitor her heart rate while exercising. This can be done by taking her own pulse or by using a heart monitor. The heartbeat should stay at around 120 beats per minute and occasionally can peak at 140 beats per minute.
After delivery, it may be a few weeks before you can return to pre-pregnancy levels of exercise. Talk to your doctor about the specifics, but usually after a standard delivery, 2-3 weeks is the norm, and 4-6 weeks after a cesarean section.
©MMII CBS Worldwide Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed