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How Pregnancy Changes Your Body

Heart and Circulatory System

What's going on: Long before you hear the pitter-patter of little feet, you'll feel the thump-thump of your heart. "Because the heart has to pump extra blood, it beats faster and harder than normal, especially when a woman exerts herself," says Ann Bolger, M.D., a San Francisco cardiologist and spokesperson for the American Heart Association. Since there are so many more blood vessels to fill (especially in the placenta, which has tens of thousands of them), and since pregnancy hormones make the tone of these vessels a bit lax, blood pressure tends to drop slightly in the second trimester. "This is why a pregnant woman may feel faint or dizzy if she stands up too fast," Bolger explains. For reasons that aren't yet clear, though, blood vessels may constrict instead of relax, causing blood pressure to rise in about 7 percent of pregnancies. The result is pregnancy-induced hypertension, or preeclampsia, which reduces blood flow to the uterus and can lead to an emergency delivery.

What to do about it: Iron is vital for the development of all those extra red blood cells, so consuming 6 milligrams (mg) a day of this mineral will help prevent anemia. To keep your heart strong and healthy during pregnancy, get regular doses of moderate aerobic exercise, and drink plenty of water before, during, and after. "Walking just 20 minutes a day strengthens your heart and lungs for labor and delivery and keeps your blood pressure down," says Bolger. Just be sure to get your caregiver's okay before embarking on a prenatal exercise regimen, and ask what your target heart rate should be. When you're working out, check your heart rate often and take a breather when it starts to inch past that number.

If you feel faint, sit or lie down and breathe deeply until the lightheadedness disappears. Finally, let your doctor know right away if you spot any of the warning signs of preeclampsia: constant, severe headaches; swelling in your face or hands; abdominal pain; visual disturbances; or sudden weight gain of more than a pound a day. Bed rest and other measures can help keep the condition under control.