Track your baby's development, week by week



Can running a fever while I'm pregnant harm my baby?

Early in pregnancy, a low fever is probably not a problem, but a high fever (over 103 degrees Fahrenheit) can be lethal for the baby.

The physiologic processes in early fetal development, such as protein activity, are temperature sensitive, and the entire fetal development process hinges on the right proteins getting turned on at the right time. If your body goes from 98.6 degrees to 103 degrees, it could keep the proteins from working properly and cause you to have a miscarriage.

Later in pregnancy, when your baby is fully formed and it's just a question of the baby getting bigger, fever isn't that much of a problem, unless it's caused by an intrauterine infection. To be safe, give your doctor a call if you have a fever that doesn't seem to be related to an illness.

Yes, running a fever can be dangerous during pregnancy. But you can reduce the risks by getting your fever down as soon as you can.

Figuring out what temperature constitutes a fever is the first consideration. For adults, a temperature taken orally (by mouth) that's higher than 100.4 degrees Fahrenheit (38 degrees Centigrade) or a rectal or ear temperature higher than 101 degrees Fahrenheit (38.3 degrees Centigrade) is considered a fever. If you have a fever, talk to your healthcare provider and see if you can identify the cause – and if treatment is needed, get started on it right away.

Your baby's normal development hinges on a particular sequence of steps that allow the organs and blood vessels to grow at the right time. That series of steps depends on proteins – molecules in the body that make important changes happen.

If your body goes from 98.6 degrees to the temperature of a fever, it could keep the proteins from working properly and contribute to a miscarriage. In rare cases, it can cause birth defects.

In some studies, fever during the first trimester has been linked to an increase in the risk of cleft palate, heart defects, and neural tube defects. These studies did not consider the underlying cause of the fevers, however, so there are questions about whether the cause for concern is the fever itself or whatever is causing the fever, such as an infection. More research is needed to sort this out.

In the meantime, taking acetaminophen as an anti-fever medication can help reduce the risks. And you'll feel better, too!

Learn about the safety of acetaminophen in pregnancy.

To minimize your chances of fever, take practical steps such as washing your hands often, avoiding contact with people who are sick, and getting a flu shot.

Studies of women who had a high fever or went in hot tubs or saunas during pregnancy have found a higher risk for neural tube defects such as spina bifida. This risk occurs mainly when the fever or exposure to high temperatures happened between the fourth and 14th weeks of the pregnancy. Developing a fever after this time, in the second or third trimester, is unlikely to harm your growing baby.

Researchers have also linked prolonged high fevers, particularly in the first trimester, to miscarriage, but the results aren't conclusive.

Rest assured that a brief fever is unlikely to do any harm and can be treated with acetaminophen. But if the fever gets really high or lasts a long time, it's best to call your doctor. When flu season rolls around, keep in mind that all pregnant women, regardless of how far along they are, are advised to get a flu shot, which can help prevent flu-related fevers.

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