Exercising While Pregnant

By Fiona McMahon, DPT

If you were paying attention to the Boston Marathon this April you probably heard about 35-year-old Amy Keil of Minneapolis who ran the 26.2 mile course while 7.5 months pregnant. Reactions to pregnant women competing at a high level run the gamut from awestruck at the mother-to-be’s sheer fortitude to furious at the seemingly blatant disregard for the health of her unborn baby. Seeing these athletes compete at high levels sparks the questions, how much exercise is safe for these women and how much physical activity should the average woman get while she is pregnant?

Up until recently, there has been a dearth of scientific studies examining the effects of high-level exercise on the health of the mother and her child. In 2012, Linda Szymanski and Andrew Satin published an article in the American Journal of Obstetrics and Gynecology examining the effects of strenuous exercise on the fetal and maternal well-being in both physically active and inactive women. In the study women were classified by self report as “non exercisers” (women who exercised for less than 20 minutes for fewer than 3 sessions a week),  “mild to moderate exercisers” (women who worked out for at least 20 minutes per session up to 3 times a week), and highly active exercisers (women who exercised greater than 4 times a week).

The women in this study participated between the 28th and 32nd week of their pregnancy. The participants ran on a treadmill with a 2% incline that increased every 2 minutes until the grade reached 12%, at which time the speed was increased by 0.2 miles per hour every 2 minutes. When the women no longer wanted to continue, they were allowed to stop and the well-being of their fetuses was examined by measuring the blood flow through the uterine and umbilical arteries, fetal heart rate, and maternal heart rate.

The women all reached a heart rate of well over 140 beats per minute, which was beyond the traditional limit on physical activity in expectant women prior to 1994. All women also exercised at a perceived exertion rate consistent for the definition of strenuous exercise. The study found that the blood flow through the uterine and umbilical arteries did not significantly change with exercise in any of the groups of women who participated in the study indicating that in short duration strenuous exercise may not be harmful to the fetus. The study did find that five women in the highly active group experienced fetal heart rate decelerations when they finished running on the treadmill. The fetal heart rate returned to normal within 2-3 minutes and did not meet the inclusion criteria for fetal bradycardia (slow fetal heart rate). The authors of this study were reassured by the transient nature of these fetal heart rate changes in the highly active group.

The work presented by Linda Szymanski and Andrew Satin provides athletes who are pregnant with some reassurance that they are not harming their baby by continuing to exercise. The authors do point out that the work presented in their article should be interpreted cautiously as it includes only one data point from the third trimester of pregnancy and should not be taken as definitive proof that strenuous exercise absolutely won’t harm an unborn child.

So you may be thinking that you absolutely have no intentions of running until exhaustion when you are pregnant, but should you still exercise? Much of the research published on activity and pregnancy says yes.

In a 2012 review conducted by Tiffany Field in infant behavior and development, exercise was found to be protective against depression, cramps, edema (swelling), low back pain, and gestational diabetes. She found the Tai Chi was particularly helpful in improving oxygen consumption, and that yoga reduced stress.

Safety is important to keep in mind while exercising when pregnant. The pregnant body undergoes a multitude of different changes that will affect your ability to exercise. During pregnancy your blood volume will increase. With the blood volume increase, the ratio of plasma to red blood cells (your body’s oxygen delivery system) will change leaving you with relatively few red blood cells compared to plasma, which will make you feel more tired more quickly. Your need for oxygen will also increase as you progress through your pregnancy. Your growing baby will also put pressure on your diaphragm making the amount of oxygen available for exercise decrease. These changes may make you feel more tired than you would when you were not pregnant and you may have to cut back the amount of activity you do.

The American College of Obstetrics and Gynecology (ACOG) advises that women who are inactive be examined by a health care professional before starting exercise while pregnant. They recommend that women try to get 30 minutes of exercise a day. They advise women with a history of pre-term labor or fetal growth restriction to reduce their activity in the second or third trimester. The ACOG recommends athletes with uncomplicated pregnancies continue to exercise as tolerated during their pregnancy.

What warning signs should you look for when exercising while pregnant? The NCAA has released guidelines on exercise in their Policy on Gender Equality. Athletes should not start exercising, or should stop exercising, if they experience vaginal bleeding, leaking of clear fluid from the vagina, headaches, chest pain, decreases in fetal movement, calf pain, muscle weakness, or breathlessness prior to exercise.

While the jury may not have completely reached its verdict on whether or not ultra intense athletic events are safe while pregnant, exercising at mild to moderate levels while one is pregnant is largely considered to be safe and to yield many benefits to expectant mothers. Keeping an open dialogue about your fitness goals with your gynecologist can help you to formulate a fitness plan that will allow you to reap the many benefits of staying active while pregnant.

Stay tuned for more Blogs on prenatal pain and leakage, postpartum pain and other conditions, and sexual health after childbirth.

Sources

  • Davenport M, Giroux I, Sopper M, et al. Postpartum exercise regardless of intensity improves chronic disease risk factors. Medicine & Science in Sports & Exercise. 2011; 951-958
  • Ferreira C, Alburquerque-Sendín. Effectiveness of physical therapy for pregnancy related low back and/or pelvic pain after delivery: A systematic review. Physiotherapy Theory and Praticce. 2013: 29(6):419-31
  • Field T. Prenatal exercise research. Infant Behavior and Development. 2012; 35: 397-407
  • Hogshead-Maker, N, Scrensen E. Pregnant and Parenting Student- Athletes: Resources and Model Policies. NCAA Gender Equity.
  • Noon M, Hoch A. Challenges of the pregnant athlete and low back pain.  Curr Sports Med Rep. 2012; 11(1):43-8
  • Szymanski L, Satin A. Strenuous exercise during pregnancy: is there a limit? American Journal of Obstetrics and Gynecology. 2012

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