Heat Regulation and Exercise During Pregnancy
Vigorous Aerobic Exercise, Overheating, and Birth Defects: Fact vs. Fiction
Scientific evidence has demonstrated a link between maternal high-fever and an increase in neural tube-related birth defects, especially in the first trimester of pregnancy. Since the fetus cannot disperse excess heat, medical professionals once speculated that the increased heat generated during vigorous aerobic exercise might cause birth defects similar to those associated with the mother's high fever.
Contrary to speculation, the slight elevation in maternal core-temperature that occurs during strenuous exercise presents no threat to the developing fetus. In fact, medical studies have consistently observed several maternal adaptations that aid in regulating body heat and that are strongly fetal protective in nature.
How Maternal Body Adaptations Protect the Fetus
- You'll notice that during exercise, you will begin sweating at lower levels of exertion than you did when you weren't pregnant; this amplifies cooling.
- As your body expands to accommodate the developing fetus, so does the surface evaporation area of your skin. Relaxation of blood vessels due to pregnancy hormones increase circulation to the body's surface areas; thus facilitating efficient cooling.
- When exercising during pregnancy, your respiration rate—how many breaths you take per minute—speeds up and your tidal volume—the amount of air you take in per breath—increases, thereby raising the amount of heat dissipated during exhalation.
PREGNANT WOMEN SHOULD NEVER USE A HOT TUB, SAUNA, STEAM ROOM, OR NATURAL HOT SPRING AS THESE MAY RAISE CORE TEMPERATURE TO DANGEROUS LEVELS.
Stay Safe and Comfortable When Exercising during Pregnancy
- Stay well hydrated during your workout; see the hydration and Exercise during Pregnancy web page for more information.
- For good air-circulation and evaporation, wear loose, comfortable clothing, constructed of loosely woven fibers or specially patented sports-fabrics that "wick away" moisture to enhance cooling.
- As your workout progresses, cool your body by removing layers of clothing as necessary.
- Avoid exercising out-of-doors when the weather is hot and humid.
- Stay out of the hot sun during your workout.
- Exercise indoors when the outside air-quality is poor.
- Bikram or other "hot" yoga styles are not recommended during pregnancy.