To prevent fetal injury, avoid sports that can involve potential contact, such as soccer and basketball. Vigorous exercise above 6000 ft (1828.8 m) and scuba diving can be dangerous for your fetus.
Unless you are a competitive athlete, avoid strenuous activity, and exercise only in moderation. You should be able to talk while you are working out. Do not exercise to the point that you feel tired.
Stop what you are doing and contact your doctor if you notice any of the following:
After your fourth month of pregnancy, avoid any exercise that requires you to lie flat on your back on a hard surface, such as sit-ups and some yoga poses. The increasing size and weight of your uterus will press on the large blood vessel that returns blood from your lower body to your heart.
As your pregnancy advances (usually during the second trimester), unstable joints, an expanding abdomen and an altered center of gravity can make you more unstable on your feet. Also, by then your uterus is mostly above the protective circle of your pelvic bones. Avoid exercises that might cause you to fall, such as skiing or roller-skating.
Swimming and brisk walking are safe exercises throughout pregnancy.
There is no evidence that exercise causes miscarriage. But if you have a history of repeated miscarriages, your doctor may advise you to avoid exercises that require your body to bear extra weight (such as running) during the first trimester.
Your baby will not be harmed if you can't exercise because of a complication of your pregnancy or an existing chronic illness or condition. You may be able to do simple exercises in bed, with your doctor's approval.