Good news: You can safely start an exercise program during pregnancy even if you've been an avid couch potato until now. If you were sedentary before you became pregnant, it's important to review your exercise plan with your healthcare provider before you begin.

Pregnancy isn't the time to try to lose weight or begin a vigorous exercise routine, but if you aren't in any of the high-risk categories, you can pursue an exercise regimen at a mild to moderate level.

Start slowly and wisely

Beginners should start by exercising 10 minutes at a time and so on, until you build up to 30 a minutes a day on all or most days of the week. Don't go for the burn and don't exercise to exhaustion. A good rule of thumb: Slow down if you can't comfortably carry on a conversation.

Be careful to eat properly and get enough fluids. Being pregnant means you need approximately 300 extra calories a day, depending on your prepregnancy weight.

Always stay cool while exercising. Wear a sun hat and layers of loose, comfortable clothing when working out in hot, humid weather. Keep a bottle of water handy to replenish lost fluids. If you’re exercising outside, be sure to wear sunblock since pregnancy can make your skin more sun-sensitive.

Safe exercises

If you're pregnant and new to the joys of physical fitness, consider:

Walking: This activity gets top honors for expectant mothers because it's safe, easy to do, and improves your cardiovascular fitness — in short, it's the perfect way to get started if you didn't exercise before pregnancy.

Low-impact aerobics classes or fitness DVDs: Look for ones that cater to pregnant women.

Swimming: This is a great form of exercise because it uses your whole body and puts little strain on your joints. An added bonus: The water supports your weight, giving you a temporary reprieve from feeling ungainly as your belly gets bigger.

Prenatal yoga and stretching: Both ease tension and help keep you flexible and strong.

Activities to avoid

High-risk sports, such as scuba diving, and activities with a potential for hard falls, such as horseback riding, downhill skiing, snowboarding, and waterskiing, are off-limits to pregnant women.

Certain other forms of exercise, such as bike riding, should be pursued more cautiously or postponed until after the baby's born. While biking enthusiasts may disagree, some experts say that biking during your second and third trimesters is dangerous because your balance isn't what it usually is, making falls more likely.

Pregnancy isn't the time to start running, either, although it's fine if you jogged regularly before getting pregnant. You may need to modify your running routine during pregnancy, though, so talk to your healthcare provider.

After the first trimester, avoid sit-ups and other exercises done while lying flat on your back — they can make you dizzy and decrease the blood flow to your uterus.

Weight lifting and other exercises that involve standing in place for long periods can also decrease the blood flow to your baby. Keep moving by changing positions or simply by stepping back and forth.

Warning signs

If you have shortness of breath before you exercise, be sure that it passes before you start. And if you have any of the following symptoms while you're exercising, stop immediately and contact your doctor or midwife if the symptoms don't quickly resolve:

  • dizziness or feeling faint
  • muscle weakness
  • headache
  • chest pain
  • calf pain or swelling
  • vaginal bleeding
  • contractions (preterm labor)
  • fluid leaking from your vagina
  • decreased fetal movement
  • rapid heartbeat while at rest