For Expectant Moms, Fitness a Routine Part of Pregnancy

What are a bunch of pregnant women doing at a 6:00 a.m. step aerobics class? Doctors say they are doing exactly what they should be doing.

"Probably the number one tip is just to use common sense," says Dr. Tammi Gregory. "[For] women who already have an exercise program, it is safe enough to continue with that routine."

Gregory says women who have never exercised before pregnancy should start out slow.

"We do have a body change, you need to do safe sports, safe activities," she says.

"It's been great. It gives me more energy for my pregnancy to go ahead and exercise," says expectant mother Lisa Rider.

Stretching is always important when you exercise, but it is especially important when you are pregnant. That is because pregnancy loosens the joints and muscles in a woman's body.

Your body lets you know when it is time to tone it down. If you are breathless, take a break. Keep your heart rate within a safe range, and drink plenty of water.

Doctors and mothers agree that safe, regular exercise during pregnancy can help in the delivery room.

"The doctor said 'Go ahead and push' and I gave it what I thought he wanted to me to give and he said 'No! Stop. Don't push that hard,' I was really strong," says Rider.

Instructor Ellen Lawson, 32, leads the class. She is pregnant with her third child.

"It's just like training for a marathon. You have to build up to it. Labor is like a marathon," says Lawson.

Doctors say a fit pregnancy also equals a faster recovery.

"Healthy muscles will heal much faster," says Gregory.

"I think the first thing I said, surprisingly, after I had my son was 'I can do this again.' It was a very easy recovery and was very quick. I really felt prepared to have my son," says Anne O'Toole, who is expecting another child.

Gregory says there is no reason why women cannot exercise all the way through their pregnancy. She insists the most important thing is to get the advice of your doctor before doing so.

Overheating can cause problems with the development of the fetus in the first trimester.

Late in the pregnancy, too much exertion can cause premature labor. Throughout pregnancy, muscles and ligaments are more prone to injury.