Hot weather may pose an obvious risk of overheating, but a fever, water bed, or vigorous exercise may cause hyperthermia too. How hot is too hot when you are expecting, and what activities should you steer clear of?
How hot is too hot during pregnancy?
Your normal, average body temperature is slightly below 37 Celsius or 98.6 Fahrenheit. Pregnancy hormones (progesterone especially) and a changed metabolism will increase the body temperature slightly, in some cases even to 38.3 Celsius or 101 Fahrenheit. Anything beyond that is too hot.
The ACOG, American College of Obstetricians and Gynecologists, says a pregnant woman's core temperature should never get hotter than 102.2 Fahrenheit. If you have a fever during pregnancy, especially in the first trimester, it's always important to take fever reducers over the counter fever reducers are safe during pregnancy, while fevers may be dangerous.
Animal studies suggest that overheating during pregnancy also called hyperthermia can be extremely risky, and can lead to neural tube defects like spina bifida. It is not quite clear how risky overheating is in human pregnancies, but there were some studies carried out on the topic. There is some evidence that significantly elevated temperatures increase the risk of miscarriage; those expectant mothers who regularly use hot tubs at high temperatures are more likely to miscarry.
Japanese research shows that mothers who were ill and had a fever early on in pregnancy had a higher risk of having a baby with anencephaly, while a study from Finland during the 1990s found that overheating in the first trimester is associated with cardiovascular malformations in a fetus. Plenty of sources will tell you that there is "no scientific evidence" that overheating during pregnancy can actually harm unborn babies, but the small sample of scientific findings we just mentioned should be quite enough to prove otherwise, all by itself. Pregnant women should avoid overheating, especially during the first trimester when all the vital organs are being formed.
Activities that carry the risk of overheating
A number of activities carry the risk of overheating during pregnancy. Out of those, a high fever is probably the most obvious one. The good thing about fevers during pregnancy is that a fever usually gets someone's attention, and most people will take fever reducers to bring it down. A recent study that suggested fever early on in pregnancy doubles the risk of having a child with autism has been the topic of much discussion, but cardiovascular problems and neural tube defects are also on the list of possible consequences.
The moral of the story?
Don't worry about the side effects of paracetamol or Tylenol during pregnancy, and be much more concerned about the possible side effects of a fever in the first trimester. Using hot tubs, taking hot baths at home regularly, or going to a sauna or sunbed are also activities that may lead to overheating and that are quite obvious, as well as easy to avoid. Hot tubs are especially risky because they keep most of your body immersed for long periods of time. That explains why there are many more warnings against using hot tubs than against having a hot bath at home.
Being pregnant in the summer in a country with a hot climate, or during a heat wave, may be just as risky. There isn't much you can do about that except turning the air conditioning on and staying out of the sun. Tanning at the beach is not a good idea during pregnancy because of overheating concerns as well as other dangers. Did you know melanoma is the only cancer than can affect the placenta, too?
Vigorous exercise during pregnancy may also lead to fetal hyperthermia. Running, jogging, and vigorous aerobics are all activities that can cause overheating, but may not if you take the right precautions. You may just be fine if you don't go running in the hot sun, take plenty of water with you and use it, and take regular breaks. Wearing loose cotton clothing is another important step you can take to prevent overheating. Low-impact exercises that don't have a risk of hyperthermia at all are safer, however. Swimming, prenatal yoga, and low-impact aerobics (in an air-conditioned environment if need be) are all safe pregnancy exercises that don't raise your core temperature too much. Swimming may actually cool you down.