Woman with thermometer sitting on the bed

Here's How To Tell If That Fever Is The Flu Or An Early Pregnancy Sign

Women who are trying to get pregnancy want to know as soon as possible whether they have a baby on board, and many report experiencing a slight fever before they’ve even missed their period. Is a fever an early sign of pregnancy? The answer is more complex than a simple yes or no.

Temperature has long been used to track fertility, as Felice Gersh, M.D., OB-GYN, told Romper in an interview. Body temperature is related to hormones, which fluctuate through a woman’s menstrual cycle. It’s why basal body temperature can be used to track ovulation.

“Progesterone is produced after ovulation and results in a small temperature elevation, which is the foundation of the basal body temperature charting,” Dr. Gersh says. “Measuring one’s temperature first thing in the morning with a special basal body thermometer was commonly done for fertility evaluations prior to the development of ovulation kits, but still continues to be utilized by many women for natural fertility planning.”

The same hormone that makes it possible to track your cycle using temperature is what causes an increase in your overall body temp early on in pregnancy, Dr. Gersh adds. But it’s not to be mistaken for a true fever.

“Pregnancy results in a far greater production of progesterone and a small further increase in temperature, which can be perceived as a fever by the woman, but actually is only a normal small temperature rise,” she says.

So, while it’s not exactly a fever, a slight uptick in your body’s temperature may clue you in to the fact that your progesterone is higher than usual. But if you find yourself with symptoms of a fever, like body chills or aches and pains, be sure to visit your doctor.

“Becoming infected with a virus or bacterial agent during pregnancy can have very dire consequences, depending on the time of pregnancy and the infectious agent,” says Gersh. “It is a rarity these days due to vaccines, but infection with the virus called rubella was well known to cause serious birth defects. Parvovirus can wreak havoc in the body of the developing baby. Flu viruses as well can be very damaging.”

Timothy J. Rafael, M.D., OB-GYN, tells Romper that women should keep an eye out for other early signs of pregnancy to indicate if that temperature increase is a fever or bun heating up the oven.

“There could be a lot of signs of early pregnancy and temperature variation can happen,” he says. “Other signs are implantation bleeding or spotting, headaches, nausea, vomiting, fatigue, and nasal congestion, in addition to different food cravings. While there can be hot flashes, it’s important for women to understand that a fever over 100.4 degrees is never normal, and with any fever, it’s important for the woman to call her provider for an exam. With a fever over 100.4, it’s an infection until proven otherwise.”

What kind of danger does fever pose during pregnancy? The Centers for Disease Control and Prevention (CDC) say that fever during early pregnancy doubles a baby’s risk of being born with a neural tube defect, like spina bifida. Fortunately, the CDC also reports that women who had fevers before or during early pregnancy but were taking 400 micrograms of folic acid daily totally bypassed that risk.

“We have to take this with a grain of salt, because neural tube defects overall only affect seven per 10,000 births in the U.S. annually, which is less than 1%, so even with double that risk, we’re still looking at a very small number that will be affected,” says Rafael. “Patients need to be treated if they’re having a fever, but the numbers are in their favor that there won’t be adverse outcomes. It’s important that if you’re not using birth control and even thinking about conceiving, take a prenatal with at least 400 micrograms of folic acid. That’s the biggest takeaway.”

If you notice yourself feeling feverish, definitely check with your doctor. If you’re not sick and trying to keep germs at bay, the CDC recommends steering clear of anyone who is sick or has an infection, washing your hands often, talking to your provider about vaccinations, and not touching the saliva of babies or other little ones (if that’s even possible, moms of multiple kiddos).


Felice Gersh, M.D., OB-GYN, founder of the Integrative Medical Group of Irvine in California, and author of PCOS SOS Fertility Fast Track

Timothy J. Rafael, M.D., board-certified OB-GYN and director of Maternal Fetal Medicine at Long Island Jewish Forest Hills