PT on the Net Research

Bikram Yoga and Pregnancy


Question:

I am looking for information on Bikram yoga, such as possible contraindications for someone who is pregnant and doing Bikram, even though it's only 90 degrees and not 110 in the class. I think it could be bad for the fetus, and I'm looking for some supportive evidence.

Answer:

Your question is very timely! I was teaching my "Training the Pregnant and Postpartum Client" workshop last week and one of the trainers said she was in a Bikram yoga class and two pregnant women stopped several times to take their temperature. They remarked that they were making sure their body temperature did not go higher than 102 degrees Fahrenheit.

It is sometimes frustrating to personal trainers that we don't get specific, black and white answers on whether our pregnant clients can do a certain activity or exercise. What we do get, however, are general guidelines based on research. It is up to us to determine how to use that information. So, with Bikram yoga, the concern is the heat of the room and how that may affect a pregnant client's fetus. Pregnancy increases core body temperature, and so does exercising. Can a pregnant woman's body get rid of this heat she is producing? This question of heat production versus heat dissipation has inspired research. Add external temperature of the environment (indoor hot yoga or outdoor in hot humid weather), and you have another variable to consider.

The American College of Obstetricians and Gynecologists (ACOG) is the organization that sets the guidelines for exercising during the pregnant and postpartum period (acog.org), and they have modified their recommendations during the last 20+ years. A great example of this is the suggested training heart rate during pregnancy. ACOG originally recommended keeping the maternal heart rate under 140 beats per minute while exercising, since an increase in heart rate results in blood being shunted away from the core to go to the working muscles, and the fear was that this would reduce the blood supply to the uterus to an undesirable stressful level. Heart rate increases by working relatively more muscles at the same time (running instead of cycling) or working harder (anaerobic intervals in spinning class). After researching, they found this was not the case, and they modified that in their 1985 committee opinion, suggesting moderate exercise intensity. Did you get that? 1985! It is amazing how many consumer publications still list the 140 beats per minute as a guideline!

The current ACOG document was published in 2002 (Obstetrics and Gynecology; 2002; 99; 171-173). Basically, ACOG suggests that pregnant women adhere to recommendations by the Centers for Disease Control and Prevention (CDC) and American College of Sports Medicine (ACSM): "In the absence of either medical or obstetric complications, 30 minutes or more of moderate exercise a day on most, if not all, days of the week is recommended for pregnant women." To me as a trainer, the word "moderate" is key. Tools like the talk test help us to determine at what intensity the client is working.

This vague recommendation from ACOG is what might be frustrating to trainers, so let's look at more feedback from them and others. ACOG goes on to say that conclusive data on core temperature is limited (Clapp 1990), with no reports of hyperthermia being dangerous to the fetus.

Dr. James Clapp, in his book Exercising Through Your Pregnancy, tells us that although the upper limit of thermal response during exercise isn't known, a rise of up to three degrees Fahrenheit (1.6 centigrade) is not dangerous (birth defects, miscarriage, etc). That means keeping the core body temperature below 102 degrees should be the focus (get your flexible rectal thermometer ready!). He mentions this as a consideration from the time the client wants to get pregnant throughout the entire three trimesters.

So back to the original question: Can a pregnant client do Bikram yoga? Three important questions to consider for any activity that your pregnant client wants to participate in are:

Besides that, a question we as trainers need to ask is: what is the risk versus the benefit of doing this activity right now? Even though I suspect your question revolves around the temperature aspect, we must also consider that ACOG recommends that each activity be evaluated according to overall risk, risk of injury, falling or abdominal trauma. Are these factors an issue in the class?

I ask my clients to consider whether they have any inkling of a doubt as to whether they should do a specific activity as even the stress in wondering is sometimes not worth it. Good luck!

References:

  1. Aaron, P., et al. Maximal Exercise Testing in Late Gestation: Fetal Responses. Obstetrics & Gynecology; 2000; (96).
  2. ACOG Committee Opinion; Obstetrics and Gynecology; 2002; (99).
  3. Clapp JF 3d. Exercise in pregnancy: a brief clinical review. Fetal & Maternal Medicine Review; 1990; (2).
  4. Clapp, J. Exercising Through Your Pregnancy; Human Kinetics, 1998.
  5. Lotgering FK, et al. Maximal aerobic exercise in pregnant women: Heart rate, O2 consumption, CO2 production, and ventilation. Journal of Applied Physiology; 1991; (70).
  6. Macphail, A., et al. Thermoregulation during aerobic exercise in pregnancy. American Family Pysician; 2002; June 15.
  7. Milunsky, A., et al. Maternal heat exposure and neural tube defects. JAMA; 1992; (268).
  8. Sady MA, Haydon BB, Sady SP, Carpenter MW, Thompson PD, Coustan DR. Cardiovascular response to maximal cycle exercise during pregnancy and at two and seven months post partum. American Journal of Obstetrics and Gynecology; 1990; (162).
  9. Wang TW, Apgar BS. Exercise During Pregnancy. American Family Physician. 1998; 57(8).