Experts agree, when you’re expecting, it’s important to keep moving: Pregnant women who exercise have less back pain, more energy, a better body image  as well as faster return to their pre-pregnancy shape. Being fit doesn’t have to mean a big time commitment or fancy equipment. some workouts are simple and can be done at home, and safe to do in each trimester.
Of course, consult with your doctor before you start any exercise program. Some women will not be able to exercise during pregnancy because of specific conditions or complications.

How do you get started?

The first thing that most newly pregnant exercisers worry about is miscarriage -- thanks to age-old myths that have women believe that a bout of strenuous exercise can harm the baby. There is no real evidence that exercise is linked to miscarriage. Heavy exercise isn't going to hurt your baby, but it will tire you more quickly than it did pre-pregnancy.

The amount of blood a woman has increases during pregnancy by about 50 percent, and her heart needs to work harder to push all that blood around -- including circulating it through the placenta, an extra organ. That means the stress on your heart will be 50 percent greater for the same exercise that you were doing before pregnancy. So you can work just as hard doing less than you did before you were pregnant.

Pregnancy isn't the time to push yourself to the max, but it's also okay -- and good for you -- to get your heart rate up with cardiovascular exercise. In the first trimester, when you're not any bigger and don't yet have balance issues, you may be able to exert yourself more if you're not too tired.

How Will you feel While Exercising During Pregnancy?

Pregnant women often notice that they feel out of breath more quickly than they used to. You may assume this is a sign that you're out of shape.

In fact, during pregnancy you're breathing 20 to 25 percent more air because you need to get rid of the carbon dioxide levels in your own blood -- and in your baby's. (Babies in utero aren't breathing on their own, but they're still producing carbon dioxide, which transfers to the mother's blood. She needs to breathe more so she can get rid of it.) So breathing more doesn't mean you're any less fit. It simply means that your body is adapting exactly as it should.

What Exercise Should You  Avoid During Pregnancy?

For women who are already in top shape, exercising during pregnancy is about maintaining their fitness, not about making fitness gains.

While there are some things to avoid, such as scuba diving, horseback riding, or any contact sport that could cause blunt-force trauma to the abdomen, there's relatively little that pregnant women can't do.

Even the longstanding prohibition against exercising on your back is somewhat of a myth It's true that lying flat on your back late in your pregnancy can cause your growing uterus to push down on the veins whose job it is to deliver blood, leading to decreased blood flow. Blood can get shunted away from the uterus, and you might feel light-headed. But performing exercises on your back for a short period (such as a series of Pilates moves) is not likely to do any harm, and you would feel uncomfortable long before your blood flow was compromised.

A Trimester-by-Trimester Guide to Exercise

First Trimester Tips

• You can pretty much continue doing exactly what you were doing before pregnancy (including lifting the same amount of weight).
• Now is a smart time to get involved in a prenatal yoga or Pilates class; it's a great habit to carry throughout your pregnancy (plus, you'll get to be around other pregnant women).
• If you feel sluggish, try decreasing either the intensity or the duration of your workout rather than skipping the workout altogether (example: drop your jogging pace by 30 seconds a mile, or cut your bike ride a few miles short).

Second Trimester Tips

• Your heart is starting to work harder to circulate all the blood you built up during the first three months. Cut back your cardio intensity by 20 to 30 percent. You'll still feel as if you're working just as hard.
• Avoid inversions (such as Downward Dog in yoga) if you feel at all light-headed.
• If you're a cyclist, consider switching to the stationary bike or to a Spinning class; your growing belly can make balancing on a bicycle tricky.

Third Trimester Tips

• Your joints are more vulnerable, so beware of heavy (15 pounds or more) weights; opt instead for more repetitions.
• Do free-weight exercises seated, if possible, because you'll want your back supported (plus it's hard to balance while standing up).
• You can continue with your cardio right up until you deliver, but don't be surprised if you can walk faster than you can jog. Many pregnant women find that supporting their belly (with something like the Belly Band) during cardio helps take the pressure off.
• Now is a great time to try swimming: You'll feel wonderfully weightless in the water, and it won't stress your joints.

 Source: Originally published in American Baby magazine.