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Exercise and Pregnancy


“What are your opinions about running and pregnancy. Does it affect it does it hurt the baby in the beginning trimester? Does it affect trying to get pregnant? There are so many myths out there. I have been training for a half marathon for the past year and have a good base of ten miles and have run 3 half marathons, everyone tells me to stop if I want to get pregnant, but I feel like I already have a good base so its not like I am overworking myself to the point of exhaustion. Any tips you have I’d love them.”


As a rule, pregnant women are encouraged to engage in regular, moderate intensity physical activity. You are correct, however, in that there are many myths surrounding exercise and pregnancy. This is partly due to the scarcity of data on the subject and the ever changing positions from the American Academy of Obstetrics and Gynecology over the years. Some of the original concerns were theoretical. These included a fear that rising a woman’s body temperature, as occurs with exercise, can cause birth defects in the developing baby particularly in the first 3 months (first trimester). This concern was based on studies done in mice in which increases in body temperature resulted in deformed or miscarried babies. This has never been proven in humans although, as you can imagine, such a study would be difficult to find volunteers. Body temperatures between 102 and 103 degrees Fahrenheit can be reached in normal modest to intense exercise under normal conditions without harm to a developing baby. Another myth associated with exercise was the fear that active muscles demand increased blood flow, blood flow that could be taken away from or stolen from the baby and placenta. This also has never been proven under typical exercise conditions. Lastly, is the fear that the excess jostling that occurs with exercise could be harmful to the baby. This may be true for situations in which the mother is exposed to major trauma e.g. motor vehicle accidents or falls, but is not true for typical non-contact exercise in an otherwise normal and uncomplicated pregnancy.

So, what are the recommendations?  As of 2009, the American Academy of Obstetrics and Gynecology has provided the following advice:

Do NOT engage in aerobic exercise during pregnancy if you have heart disease, lung disease, an incompetent cervix, twins or greater, persistent bleeding in the second or third trimesters, a placenta previa after 26 weeks (a placenta that is covering the birth canal of the cervix), premature labor during pregnancy, ruptured membranes, preeclampsia or pregnancy induced high blood pressure, severe anemia, poorly controlled Type I diabetes, extreme morbid obesity, extremely underweight (BMI < 12), a baby that is not growing properly (known as intrauterine growth restriction), poorly controlled seizures, poorly controlled hyperthyroidism, you are a heavy smoking or are extremely unfit to start with.

They also go on to suggest that pregnant women who are exercising stop and check with their obstetrician if they notice any of the following: vaginal bleeding, undue shortness of breath, dizziness, headaches, chest pain, muscle weakness, calf pain or swelling, preterm labor, the baby has stopped moving or leakage of amniotic fluid. Many of these symptoms can suggest other serious pregnancy-related problems that exercise may make worse.

In general however, recreational and competitive athletes with uncomplicated pregnancies can remain active during pregnancy but should modify their usual exercise routines to allow for frequent breaks, get the proper nutrition for their level of exercise, avoid prolonged exhaustive activity, avoid dehydration, avoid working out in extreme weather conditions, and pay close attention to what their bodies are telling them. Those in excellent physical condition prior to pregnancy can expect to continue to exercise at a high, although not necessarily competitive, level throughout pregnancy provided no pregnancy related complications arise. Previously inactive women can safely begin a walking or mild wateraerobics program but should not embark on a vigorous exercise program for the first time during pregnancy.

The answer to the second part of your question regarding curtailing exercise if you want to get pregnant is that it depends. If your menstrual periods have been regular off birth control pills throughout your running regime and your nutrition has kept pace with your level and intensity of activity, then you should have no problems remaining active while trying to conceive. If on the other hand you have experienced months of missed menstrual periods, your nutrition is suspect and/or your BMI is less than 20, you may have difficulty getting pregnant. Provided your partner has no infertility issues of his own, if you have gone 1 year with spontaneous unprotected intercourse without getting pregnant you should be evaluated for causes of infertility. One part of your infertility management may require that you back off on your running significantly and increase your caloric intake. This is not easy advice for most avid runners but it depends on your priorities.

Hopefully this answers your questions and will be helpful in planning for a healthy, active and procreative life.


by Steve Scharmann – MD, Sports Medicine, Family Practice | Competitive Runner/Triathlete

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This entry was posted on Wednesday, August 17th, 2011 at 4:34 pm and is filed under Training. You can follow any responses to this entry through the RSS 2.0 feed.

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