There is no doubt that exercise really benefits the vast majority of pregnant women, both mentally and physically. But of course, there are some situations in which pregnant woman are genuinely better off avoiding exercise. How do you know if this is you?
If you are a healthy pregnant women with no complications, you normally have no reason to avoid prenatal exercise. Still, you may face situations during which working out makes you feel fatigued, and your body tells you to stop. You should listen to any warning signs your body sends you, and stop as soon as anything hurts, or you just don't feel right. Bleeding should never be ignored. Stop exercising until you see a doctor. Women who are obese when they get pregnant, or who just didn't exercise at all, should be careful and not start exercise programs without consulting their doctor. Talk about exercises that are gentle and gradually build your strength.
Women who have high-risk pregnancies should quite obviously stay away from working out, unless their healthcare provider explicitly gives you the green light. High risk pregnancies could mean expecting twins or triplets, that you have an incompetent cervix, or a history of preterm labor. Expectant moms who are on bed rest should quite obviously stay away from working out.
If you have any questions about what exercises are safe during pregnancy and what types of workout are best left for after pregnancy, you should always talk to your doctor or midwife who knows you and your personal circumstances. In general, walking, swimming, cycling, and low impact cardio exercises are always best for pregnancy, and even for women who were not very fit when they conceived. Fitness freaks who are used to working out all the time can also usually continue with their normal exercise regime, with some modifications.