Thermoregulation in pregnancy

Interestingly, just today someone told me I shouldn’t exercise because the increased body temperature will harm the baby.

I’ll add that to the other 345,423,234 things that are going to harm the baby)… Actually, no, I’ll look at the literature instead…

One study looking at the body’s temperature response to exercise found that from pre-conception (before pregnancy) to postpartum (after delivery), the body’s temperature increase in response to exercise declines continuously. The authors hypothesise that this temperature response is protective for the embryo and foetus.

Animal lovers… don’t read this paragraph. Another study exposed pregnant ewes to both hot and cold temperatures and to treadmill exercise (I don’t know how they got them on the treadmill, I used to have difficulty with humans when I worked as a personal trainer…).  Anyway, they found that in hot temperatures, the temperature rose less in the foetus than in the mother, and in cold temperatures, the temperature fell less in the foetus than the mother. It is summarised that thermoregulatory strategies used by the pregnant ewe for thermoregulation during heat or cold exposure appear to protect the fetus from changes in its thermal environment. Hmm, a similar finding to the previous study.

OK, back to studies on humans. Some researchers persuaded a group of women in their 25th week of pregnancy to cycle on land and in the water (let me think… cycling like a lab rat in the water vs. ice cream and milo on the sofa… the decision just isn’t that difficult for me).  They found that normal pregnant women can maintain thermal balance whether on land or in water and summarise that for normal, average fitness, pregnant women who wish to participate in a moderate exercise program, heat stress is probably not a major concern.

One final study caught my attention; it was entitled “the changing thermal response to endurance exercise during pregnancy“. This study design is awesome, and I quote “rectal temperature was monitored in 18 recreational athletes before, during, and after 20 minutes of continuous exercise before conception and every 6 to 8 weeks during pregnancy”. OK, I know this paper proves a valuable point, but these women are brave – they not only exercise during pregnancy, they do it with a probe up their asses. Why does this episode from South Park spring to mind? Again, I digress, the study found that there are changes in resting body temperature, the threshold at which you sweat, and venous capacitance (how much blood your veins hold) that begin early in pregnancy. Final line: “the magnitude of any exercise-associated thermal stress for the embryo and fetus is markedly reduced by the maternal physiologic adaptations to pregnancy”.

Well, I feel reassured that the pregnant body seems to take pretty good care of the baby… even so much as to regulate baby’s temperature. Ah, the things a mother does…

Lindqvist PG, Marsal K, Merlo J, Pirhonen JP. Thermal response to submaximal exercise before, during and after pregnancy: a longitudinal study. J Matern Fetal Neonatal Med. 2003 Mar;13(3):152-6.
 Laburn HP, Faurie A, Goelst K, Mitchell D. Effects on fetal and maternal body temperatures of exposure of pregnant ewes to heat, cold, and exercise. J Appl Physiol. 2002 Feb;92(2):802-8.
 McMurray RG, Katz VL, Meyer-Goodwin WE, Cefalo RC. Thermoregulation of pregnant women during aerobic exercise on land and in the water. Am J Perinatol. 1993 Mar;10(2):178-82.
 Clapp JF 3rd. The changing thermal response to endurance exercise during pregnancy. Am J Obstet Gynecol. 1991 Dec;165(6 Pt 1):1684-9.

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