A Dietitian's View

But pregnancy isn't the time to start a running routine. Pregnancy's also not the time to start training for a marathon, a triathlon, or any other race. The first trimester is when the baby's major organs are forming, and overheating's a real issue. If a woman's core temperature gets too high, it could cause problems with the baby, so why risk it?

Whether you're pregnant or not, running can be hard on your knees. During pregnancy, your joints loosen, which makes you more prone to injury. So unless you're an avid runner, you should probably steer clear of this form of workout at least until after your baby arrives.

First trimester tips
Follow the usual precautions, such as drinking lots of water before, during, and after your run. Dehydration can decrease blood flow to the uterus and may even cause premature contractions.

Wear shoes that give your feet plenty of support, especially around the ankles and arches. Invest in a good sports bra to keep your growing breasts well supported.

Second trimester tips
Your center of gravity's shifting as your belly grows, leaving you more vulnerable to slips and falls. For safety, stick to running on flat pavement.

If you lose your balance, do your best to fall correctly. Try to fall to your side or on your behind, to avoid trauma to the abdomen. Or put your hands out to break your fall before your abdomen hits the ground.

Consider running on a track as your pregnancy progresses. Not only is the track surface easier on your joints, but you may feel safer running somewhere where you won't get stranded in case of an emergency.

Third trimester tips
Be as careful as you've been during the first two trimesters. And remember: If you feel too tired to go for a run, listen to your body and take a break. Being sedentary is unhealthy, but pushing yourself too hard is also harmful.

Most avid runners find that their jogging pace slows down considerably during the third trimester — a fast walk may be a better choice as your due date approaches.