If you could jog 3 miles (or exercise vigorously for 35 minutes) without stopping and feel ok, you're in GOOD shape. If you could walk 2 miles (or do light exercise for 35 minutes) at a brisk pace and feel ok, you're in OK shape. If you didn't exercise much, you're in POOR shape.

If you're in GOOD or OK shape, exercising while pregnant will be much easier than if you're in POOR shape. But if you're in POOR shape, all is not lost, it still makes sense to exercise, provided it's done the right way.http://www.webmd.com/baby/baby-beginnings-6/exercise-during-pregnancy

Women in their first trimester may be experiencing typical “morning sickness”, which generally can happen at any time of the day. Mild nausea is normal, and exercise can be undertaken at times when the woman feels like exercising. Those experiencing severe and constant nausea should not exercise and should be talking to their doctor.

The second trimester is often called the honeymoon period of pregnancy, most moms feel better and it's generally a good time to pick up the exercise regimen. If you weren't able to exercise during the first trimester, you'll need to start slowly, even if you were in good shape prior to becoming pregnant. http://www.webmd.com/baby/features/exercise-during-pregnancy-myth-vs-fact

The third trimester is the time when the baby begins to grow very quickly and the woman's body undergoes the most changes. High impact exercise, like running, will become increasingly difficult and lower impact exercise, like swimming or stationary cycling, is a better idea. http://www.webmd.com/baby/features/exercise-during-pregnancy-myth-vs-fact

Here's a list of low impact exercises that many women can do while pregnant:

1. Swimming
2. Water Aerobics
3. Stationary Cycling
4. Walking
5. Elliptical Machines
6. Yoga
7. Light Weight Lifting
8. Cross-country Skiing

Here are exercises NOT recommended

1. Contact Sports (football, basketball, soccer, beach volleyball)
2. Endurance Sports (marathons, rock climbing)
3. Horse-back Riding
4. Downhill Skiing or Snowboarding
5. Surfing

During pregnancy, a woman's body produces a hormone known as relaxin. This helps to loosen joints for delivery, but it can also increase the risk for injury during deep joint exercise such as squats and lunges. http://www.webmd.com/baby/baby-beginnings-6/exercise-during-pregnancy

If you're in good shape, you can exercise 3-5 times a week (a couple days of rest are a good idea), and for longer intensities, up to about 45 minutes. Again, listen to your body and don't put undue stress on it.

You should not perform an exercise that requires you to lie on your back, particularly after the first trimester. If you feel nauseous or dizzy while exercising, stop. If you experience any type of bleeding or unusual pains, call a doctor immediately. http://www.webmd.com/baby/baby-beginnings-6/exercise-during-pregnancy

Write down your exercise plan and expect it to change as your body changes. Generally, you'll need to reduce your level of exercise in the last couple months of your pregnancy. Before starting your plan, take it to your doctor and make sure they agree with it.