I always found exercise beneficial when I was pregnant. Nothing too strenuous, of course, but a brisk walk, swimming and the easier yoga poses get the blood running and rid you of that dull, lethargic feeling that sometimes accompanies pregnancy.

Forbes Health Tips agrees.

Assuming your doctor approves, exercise can help keep you healthy and feeling good during pregnancy.
While you should avoid strenuous activity, light exercise can offer many benefits during pregnancy.

Is exercise dangerous? Not if you do it in moderation. The Pregnancy Blog at Families tells us:

There are things you can do to make exercise even more safe. The first step to safe exercising is to choose the right type of exercise routines. Low impact workouts are generally safer for you and the baby than a high impact work out routine. Some good low impact choices include yoga, walking or swimming. Prenatal exercise classes are usually low impact and safe choices.

Exercise during pregnancy can increase energy, improve posture and strengthen muscles, reduce stress and help you control your weight.