Expect to slow down in the last half of the third trimester, and remember that you may have a hard time catching your breath. Your body will change in a number of ways to accommodate the growing fetus. Your ligaments get looser from hormonal changes so your pelvis can enlarge during delivery. Your center of gravity changes, moving forward due to the weight of the baby and of the increased size of your breasts, making any exercise that involves balance, like skiing, much more difficult. Although it's best to remain active, there are certain sports that should be avoided during pregnancy.
Most babies grow well even if their mothers exercise.
Some studies have suggested a bit less body fat among the infants of women who exercise strenuously during pregnancy. If you experience heat exhaustion or your doctor finds that the baby isn't growing normally, it's best to stop working out until after your delivery. Staying in shape through walking and swimming has dozens of benefits in pregnancy. It burns calories so that you can keep your weight in check and helps you digest food more easily and avoid constipation. Exercise improves circulation and keeps your body from retaining fluid and decreases your chances of getting varicose veins.