For years people thought if you were pregnant you could not do anything physically active for fear of endangering the fetus. Exercise especially was strictly forbidden because doctors feared that the motions and movements would jar the fetus and cause damage to it. So, it was recommended that pregnant women rest comfortably for nine months.

However, now, science has shown that exercising actually makes for an easier pregnancy and delivery, and often helps babies to be healthier as well.

The truth is that while there was a time doctors felt women should not be active, most were anyway because there is really no such thing as maternity leave in most of the world, and in some instances if women became inactive it would mean there would be no food, etc. for their family.

So, as you can see, exercise is essential, but let's talk about exercising during the third trimester. This is the last few months of pregnancy. Your baby is growing really fast and you are getting bigger and bigger. Should you exercise? The answer is yes, with some stipulations. Exercising is going to help alleviate things like lower back pain and fatigue, and will help you rest better, etc. so do not cut it out of your routine, however, do follow these basic guidelines:

Start slowly. Even if you have exercised through the whole pregnancy, you need to be more careful during the last trimester. You can maintain the same level, but you need to listen to your body more. If you start to feel like it is too much, then it probably is, and you need to slow it down or cut back. So, be aware of your limits, and do not push your body so hard that it hurts, this is not good for you or the fetus.

Monitor your heart rate and breathing. During the third trimester it is important to pay attention to how high your heart rate gets. It is important to note that the fetal heart rate is tied to your own, as yours goes up, so does theirs, and the same goes for down. So, keep your heart rate below 140. Also, do not let yourself get too breathless. If you can't talk without a problem, you are working out too hard. You have to consider the health of your baby, and while you might want to get a little more toned, it can hurt the baby to have your heart racing you be gasping for breath. So, buy a heart rate monitor, and adjust your exercise levels to a point where you can breathe easier.

Avoid exercising at extreme altitude or in hot, humid environments. Your body temperature can affect the baby, and you do not want your fetus to overheat as it will affect its brain. Also, too high of altitudes means less oxygen for baby.

Be Careful. When you get a little further into the third trimmest, adjust the level of exercise intensity, you are heavier than you were before, and thus impact is harder, and harder on your body. So, be careful.

Do not stretch to much. When you first get pregnant your body is flooded with a hormone called relaxin, which helps with the expansion of the uterus, but also induces hyper-flexibility in the muscles and joints. Many pregnant women strain muscles and ligaments during pregnancy due to increased flexibility. Stretch, but not too much.

Avoid ballistic movements, such as jumping or running. They can strain the pelvic floor, which is already supporting more weight than ever before.

Do Kegel exercises daily. This is hugely important, and if you don't do them you will wish you had. The pelvic floor supports the bladder, uterus, and intestines, and when you are pregnant the weight of the uterus can stretch it out and often your bladder or intestines will drop down. This is a problem later, many elderly women suffer from incontinence because of this. So, prevent the problem. Contract your PF muscles (which is like stopping the flow of urine). Tighten and relax the muscle quickly several times a day.