Being fit does more than minimize weight gain. It can make labor and delivery easier and more comfortable, build bone and muscle, lift your mood, boost your energy level, reduce backaches, constipation, bloating and swelling, and even minimize stretch marks.
"It's very important to stay physically active during pregnancy," says Melody Bruce, an obstetrician-gynecologist with OB/GYN Health Center Associates in Troy, N.Y. and medical director for Northeast Women's Health Services.
Pregnant women, though, should always consult with their doctor or midwife about the level of exercise appropriate for them, Bruce stresses.
She estimates that 20 to 30 percent more pregnant women are working out today than were five years ago. One of the reasons, she says, is the availability of classes for yoga and Pilates, an exercise method that strengthens and lengthens muscles.
"The benefits are endless, and an active pregnant women is likely to feel much better mentally and physically," Bruce says.
It helped Jean Dempsey, 31, get through her most recent pregnancy. She ran on a treadmill five days a week until her seventh month. Then she walked.
"I was more energized," Dempsey says. "It felt better knowing I was actually doing something and not a slug sitting on the coach eating things."
Like anyone else, there were days she was less motivated, especially during the first month.
"Sometimes I was just so tired and didn't want to move, but always felt so much livelier afterward," says the resident of Niskayuna, near Albany. That energy is still with her seven weeks after giving birth to her second child.
Thinking on exercise during pregnancy has evolved over the past two decades, Bruce says.
"Twenty years ago, women limited their activities, especially in the first trimester," Bruce says.
The misconception that exercise could cause bleeding or miscarriage kept pregnant women idle. But as physicians, and the public, learned more, they realized most exercise, aside from anything high-contact or high-impact, is safe, even valuable.
Marathon running and rugby are out of the question, of course, but swimming, jogging and yoga are ideal, Bruce says. And Pilates has become increasingly popular with pregnant women in the last few years, says Sally Jones, site director with AmericanBaby.com.
Women who worked out regularly prior to pregnancy can generally stick to their routine, as long as they don't overdo it, experts say. Those trying exercise for the first time should stick to basic, low-impact activities. Start with a walk.
"It's fabulous for everyone," Jones says. "It's low-impact, you can do it with friends, it's free and it allows you to go at your own pace."
Calisthenics, light weight training (nothing heavier than 10 pounds) and various back and pelvic exercises are especially important for core stabilization, says Kellie Fox, a physical therapist with St. Peter's Hospital in Albany.
Pregnant women often experience back pain. Strengthening the lower back muscles with sit-ups (first trimester only) or stretches (often done with a medicine ball for support) can improve posture and ease the lower-back discomfort during pregnancy and delivery.
But sit-ups and other exercises requiring you to be flat on your back, should be avoided during the third trimester, Fox says.
"The weight of your growing baby and your uterus might impede blood flow to your heart, leading to dizziness and possibly fainting," says Ann Douglas, the author of The Mother of All Pregnancy Books.
Throughout the pregnancy, Fox also recommends Kegel exercises -- contracting and releasing the vaginal muscles -- to prevent incontinence.
Most exercises, she says, help prevent constipation by increasing movement in intestines.
Yoga teaches proper breathing techniques (useful during labor) and is great for strengthening, often helping to improve muscle tone, Fox says.
All exercises, though, should be done with some level of caution.
Hormonal changes make bones and joints more susceptible to injury, so moderation is important, Fox says.
"Your breathing should feel comfortable enough that you can still carry on a conversation while working out," Jones says.
Many of the signs that you should stop exercising are similar to the indications for those who aren't pregnant.
"If you start to feel dizzy, have a shortness of breath or have any pain, you should stop immediately," Jones says. If vaginal bleeding or any kind of discharge occurs, women should not only stop, but notify their physician.
And keep the water bottle handy. Hydration before, during and after exercise is essential.
Pregnant women should wear comfortable sneakers and a well-fitting bra.
"Breasts get bigger and heavier during pregnancy," Douglas says. "If the bra you're wearing doesn't provide enough support, you could overstretch and permanently damage the ligaments that support your breasts."