If a pregnant woman eats a well-balanced diet, she will probably gain between 25 and 35 pounds during pregnancy. Especially during the third trimester, additional calories and protein are needed because the baby is growing rapidly. Also, increased calcium is needed to fill both mom a baby's nutritional needs. Unless you're having difficulty with the pregnancy, exercise is essential. Regular exercise is encouraged even if you didn't exercise regularly before becoming pregnant.
Moderation is the key.
Choose something that you enjoy doing and stop when you are uncomfortable or tired. Exercise slowly and gently to prevent tiredness or strain. There are exercise programs designed just for pregnancy and postpartum health. Don't smoke and avoid secondhand tobacco smoke. Smoking during pregnancy exposes your developing baby to the same cancer-causing chemicals you inhale.