At 29 weeks pregnant, Shelly Fabrizio tries to stay fit. She has switched from jogging to walking to ease the stress on her body, takes a yoga class at the Ann Arbor Lamaze Childbirth Preparation Association, and is aware that she has to be especially careful when exercising in the summer heat.

“I do find that I overheat more now, more so than before I was pregnant,” she says. “Another thing that I’ve noticed on the warmer days is swelling in my feet, so I definitely have to take it easy, relax, elevate my feet, and make sure I’m drinking enough water.”

Those are all good ideas for pregnant women who want to stay both fit and safe during the heat of the summer. Pregnant women don’t have to avoid exercise just because it’s hot outside -  but they do have to be especially careful to regulate their body temperature and hydration levels, and to take into account their changing bodies, says Amy L. Tremper, M.D., clinical instructor in the Department of Obstetrics and Gynecology at the University of Michigan Medical School.

“It’s very important when you’re pregnant to regulate your temperature. If your core temperature gets too high, we think there can be fetal damage,” she says. “You need to not get as hot as you would normally, so try exercising earlier in the day when it’s cooler. Stay hydrated. And be aware of ways to dissipate heat in other ways, such as wearing loose clothing and allowing yourself to sweat.”

With those cautions in mind, exercising is vital to the health of a pregnant woman, Tremper says.

“For your health and your physical and mental well-being, for your ability to carry the pregnancy well and to feel comfortable during it, exercise becomes a very important factor,” she notes. “It will help maintain your body weight during pregnancy and will help prevent and control gestational diabetes [pregnancy-induced diabetes]. We like women to gain between 25 and 35 pounds, and increasing your metabolism by exercising is certainly going to help you not to gain more than that.”

As the extra pounds are added, a pregnant woman can experience balance problems, an altered center of gravity and a general slow-down in their movements. While the level of activity slows with most women in their third trimester, Tremper notes that it is still important to keep up some level of exercise.

Swimming is at the top of her list of recommended exercise, especially in summer when pools are more available. One of the main benefits, she says, is being able to exercise with little or no impact on the body.

“When you’re swimming or doing water aerobics, it’s extremely beneficial because of the hydrostatic pressure -  the pressure that the water puts on your body,” Tremper says. It’s almost like being in a big support stocking.”

People who regularly jog may need to slow down to a walk, she advises, and a high-impact aerobics class can be changed to low-impact.

Tremper recommends paying close attention to your breathing when you’re exercising because shortness of breath probably will occur sooner than usual when you’re pregnant.

“Part of the reason for that is somewhat mechanical: as your uterus grows, it pushes up against your diaphragm, and your diaphragm actually goes up about four centimeters by the time you’re in your third trimester,” she says. “So there’s a little less room up and down. There is room for expansion on the sides, and that’s why a lot of women have some rib pain -  your ribs actually expand to the side to help accommodate the lungs.” Several deep breaths can help relieve the discomfort.

Other tips from Tremper for pregnant women to stay healthy when exercising during the summer:

• Stay hydrated. Pregnant women in all states require more fluids, especially when they are exercising in the heat.
• Shoes that fit properly also are key, since pregnant women’s feet tend to swell, and grow even larger when they are warm.
• Wearing two sports bras might relieve some of the pain of exercising, as a pregnant woman’s breasts often grow larger.
• Be careful when stretching. When a woman is pregnant, a hormone causes the loosening of the ligaments of her body. It’s designed so the pelvis can open more during childbirth, but it also can loosen the ligaments of the knees and hips. She says pregnant women should avoid stretching to the point of resistance.
• Monitor your heart rate. Watch for signs of dizziness, excess heat release, increasing fatigue and a “racing” heart or irregular heart rate.

University of Michigan Health System