Overview

A fever is part of your body’s immune response as a natural defense to infection. The risks and benefits of fever during pregnancy are different than those of someone who is not pregnant. Running a fever during your pregnancy can be scary. Studies have linked maternal fevers to complications like autism, neural tube defects, oral clefts, and congenital heart defects. The best way to alleviate any fears or unknowns is to educate yourself about what temperature constitutes a fever, when to call your doctor or midwife, and what to do if you get a fever during your pregnancy. It is common to take over-the-counter medicine to reduce a fever. Over the years, attitudes towards the use of medications like acetaminophen have evolved. While doctors have long considered this safe, more recent research raises questions about taking this over-the-counter medication during pregnancy. 

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This article examines fevers in adults and specifically in pregnancy. Some of the guidelines are different for children, especially a newborn. We are also not discussing intrapartum fever, which is a fever that occurs during labor.

How We Regulate Body Temperature

Your body has a temperature set-point that regulates your temperature. An increase in your set point causes a fever. Your hypothalamus, a part of your brain, acts as your body’s thermostat and is responsible for increasing your body’s temperature. When your set-point changes, your hypothalamus triggers changes in your body to raise or lower your temperature. Your hypothalamus is responsible for creating muscle contractions and shivering, which causes your body to produce more heat and conserve heat so your temperature will increase to match your internal set point. It also releases epinephrine (or adrenaline) which can increase your temperature. 

Hyperthermia

Hyperthermia occurs when you have a high temperature without an actual fever—activities like working out cause your temperature to go up. You do not have a fever because your set point has not increased. You are just exerting energy, creating heat, and as long as you can cool down, it is okay. 

The risk of hyperthermia is the reason you may have heard that you should avoid hot tubs during pregnancy. You want to avoid overheating. In a really hot bath or a hot tub, when you submerge your body in water, your body cannot sweat to cool off, which may put you at additional risk. You can take a bath during your pregnancy, just don’t make it scalding hot, and you know when you are getting overheated. Pay attention to the temperature and how you feel. If you would like to enjoy a warm bath, you can. 

In hot tubs, saunas, steam rooms, you have less control over the temperature, and those tend to be quite hot. To see the evidence on hot tubs and saunas, see this article. If you like to practice Bikram yoga – there is also an episode examining the research and evidence on heated yoga. The research on fevers and how they can affect your baby also applies if your body temperature is raised because of your environment.

Running a Fever 

A fever is not a disease, virus, or sickness in itself. A fever is often a side effect of another illness or condition. Often it is part of your body’s immune response as a natural defense to infection. Many different diseases ranging from mild infections to something more severe like appendicitis can cause a fever. The common symptoms of a fever are high temperature, sweating, shivering, fatigue, headache, muscle aches, and dehydration.

Normal Body Temperature is 98.6 °F or 37 °C, Right? 

Where did this number come from? The “normal” temperature of 98.6 °Fahrenheit or 37 °Celsius came from Dr. Carl Wunderlich. He was a medical director at a hospital in Germany in the 1800s, and he oversaw the taking of vital signs on some 25,000 patients. He took the data of the temperatures taken from all of these patients and determined the average temperature of the normal human being was 98.6 °F or 37 °C. I first heard about this on a podcast called Freakonomics. There were questions about the thermometer’s accuracy, which was a couple of degrees off. It turned out he was taking temperatures in patients’ armpits, which is also not the most accurate. The takeaway, s that 98.6 °F is not evidence-based. Your body temperature varies based on many external and internal factors. Plus, your temperature fluctuates throughout the day. 

What Temperature is a Fever? 

There is not a magic number that everyone agrees upon globally. The Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists define a  fever as 38 °C 100.4 °F. Overall, a fever could be considered a temperature over 37.5-38.3 °Celsius or over 99.5-100.9 °Fahrenheit.

Accuracy of Taking Your Temperature

It makes a difference where you take your temperature. Different parts of your body will register slightly different readings. Rectal is the most accurate and is considered a central temperature. I am going to assume that you are not taking your temperature rectally. It is more likely that you are taking a peripheral temperature from either your forehead, mouth, or ear and possibly under your arm.

The Cleveland Clinic recommends adding ½° to 1°F (.3°C to .6°C) to oral and axillary temperature readings for the most accurate number. Please ask your doctor or midwife what they consider a fever so you know what number on the thermometer you are looking out for if you do run a fever. 

Types of Thermometers

You can use digital thermometers orally, rectally, or in an armpit. Tympanic thermometers are placed in the ear. Temporal artery thermometers measure the temperature from your forehead.

If you happen to have an old glass thermometer in your home, these are not recommended because they contain mercury and can break. If you need to dispose of an old mercury thermometer, it is hazardous waste, so you need to look into how to dispose of that correctly in your area.

The cost of thermometers has come down, and you can find an accurate thermometer at a very reasonable price. Digital thermometers are the least expensive. If you do not own a tympanic or temporal thermometer, now is an excellent time to buy one. While you will need to take your baby’s temperature rectally for the first few months, the thermometers that take a reading from an ear or forehead are very convenient once your baby is about three months or older.

Fever Phobia

There are a lot of misconceptions and fear around fevers. Fever phobia was a term coined in 1980 to describe parents who have inaccurate beliefs about the potential harms of fevers in their children. Concerns about brain damage, febrile seizures, and death induce anxiety about rising temperatures. There is a lot of evidence that fever phobia still exists today and even evidence that some health care providers have fever phobia. There are varying opinions on whether you should treat a fever or let it run its course. The risks and benefits of fever during pregnancy are different than those of someone who is not pregnant.

Studies on Fever During Pregnancy 

One study made headlines that there is a link between maternal fever in pregnancy and an increased risk of the baby developing autism. This study notes that 20% of pregnant women experience at least one fever during their pregnancy. This data was before COVID-19, and those numbers may be even higher since fever is a common symptom of COVID-19. This study pulled data from the Norwegian Mother and Child Cohort Study, which included over 114,000 children over a decade. Not all of those participants met the criteria for this study, but it was a large sample size. 

The headlines in articles about this study stated that fever increased the risk for ASD by 34% or even more for women who had three or more fevers after the first trimester. Before you panic, like I did when I first saw these headlines, and before I dug into the study, you must keep in mind relative risk and absolute risk. 

That 34% or more increase is relative. The absolute risk in this study of a child having autism went from .6% overall to .7%. Yes, it is an increase, but I want to be clear that if you get a fever, it does not mean that your child will have ASD. Overall, this study may show a correlation, but it does not show causation. ASD is a spectrum disorder, and there is so much we do not know about it. 

A review and meta-analysis that included 46 studies found maternal fever was associated with neural tube defects, oral clefts, and congenital heart defects. Overall they did not find an association between maternal fever and miscarriage, stillbirth, or preterm birth. Eight of the included studies showed a protective effect of using an antipyretic medication to bring down the fever. Two studies showed an increased risk with the use of an antipyretic. So there were some conflicting results among the studies included as to whether you should use medication to reduce your fever.

There is still so much we do not know about how fevers can affect a baby in utero. There is no universal temperature or length of a fever that is known to be harmful. We do not know exactly what impact a fever could have, and it is dependent on when it occurs or how long it occurs. There is a big difference between running a fever of 100 °F (37.8 °C)for an hour and running a fever of 103 °F (39.4 °C) for a day or longer. There are a lot of questions that scientists are still working to answer. 

Preventing a Fever

Ideally, you avoid getting a fever in the first place. The number one thing you can do to prevent a fever is to stay healthy. There are separate episodes on supporting and boosting your immune system during pregnancy—basic things like eating well, getting enough sleep, and staying hydrated go a long way. Also, making sure you are taking a high-quality prenatal vitamin is essential. Actions to avoid illnesses that could cause fever-like influenza or COVID-19, like frequent hand washing and being mindful about not touching your face, may also limit your risks.

What to Do if You Have a Fever 

Despite taking precautions to stay healthy, you may find yourself with a fever at some point in your pregnancy. The first thing you want to do if you have a fever is to take stock of everything going on with you. Take your temperature and see what it is; record the temperature and the time if you need to refer back to it. Also, take note of any other symptoms or signs of illness like colds, flu, or COVID-19.

If you have a fever, you should reach out to your doctor or midwife. A great question to ask at the next prenatal appointment you attend is what your care provider considers a fever and when you should call them. Other signs that may signal that it is time to contact your doctor or midwife are if your fever persists more than 24 hours with abdominal pain, rash, or nausea. This isn’t a complete list. If you want to call your doctor or midwife or are concerned at all, please do. You should be comfortable reaching out to your care provider if you are concerned, and you should have a number you can call if you need to reach someone outside of normal business hours.

If you have a fever, something is triggering an immune response, and you should be taking it easy. This is not the time to exert energy. You want to make sure you are staying hydrated. You lose more fluids when you run a fever, and staying hydrated is essential.

You can take measures to cool off, like running a washcloth under cool water and putting that on your forehead or taking a tepid bath or shower. You should be wearing light cool clothing and don’t bury yourself under a ton of blankets. 

Over-the-Counter Medications to Reduce a Fever 

It has become very common to take over-the-counter medicine to reduce a fever. Before taking anything, even over-the-counter medication, you need to run it by your doctor or midwife. Drugs that reduce fever are called antipyretics. Ibuprofen and acetaminophen are both fever reducers, and there are some questions about taking these over-the-counter medications during pregnancy. 

Ibuprofen

Ibuprofen is an NSAID (nonsteroidal anti-inflammatory drug). NSAIDs also include aspirin and some other pain relievers. Ibuprofen is usually not recommended during pregnancy. The FDA recommends pregnant mothers avoid ibuprofen after 20 weeks because it can result in low amniotic fluid. There is also evidence that ibuprofen and NSAIDs can increase your risk for miscarriage early on in your pregnancy.

Acetaminophen

Acetaminophen may also be referred to by the brand names Paracetamol or Tylenol. There are more than 600 over-the-counter medications that include this drug as an active ingredient. Typically, medical professionals prefer acetaminophen over ibuprofen during pregnancy. Acetaminophen has long been thought to be safe during pregnancy. As a result, up to 65% of pregnant mothers reported using acetaminophen at least once during their pregnancy. Unfortunately, there is some recent research that may be challenging the safety of this drug in pregnancy.

In one study, researchers related an increased risk for asthma in children to maternal use of acetaminophen during pregnancy. Another study in the Journal of American Medicine found an association between acetaminophen use during pregnancy and behavioral problems in children. More recently, 91 scientists, clinicians, and public health officials released a consensus statement cautioning against the use of acetaminophen during pregnancy. They examined many studies in both humans and animals. They found the use of acetaminophen might alter fetal development, which could, in turn, increase the risks of certain neurodevelopmental, reproductive, and urogenital disorders. The professionals behind this statement called for agencies like the FDA and obstetric and gynecological societies (like ACOG) to review the evidence and reevaluate the risks of this drug. This statement has an in-depth analysis of available research.

Days after this statement cautioning against the use of acetaminophen was released 9/23/2021, ACOG released its statement that “This consensus statement, and studies that have been conducted in the past, show no clear evidence that proves a direct relationship between the prudent use of acetaminophen during any trimester and fetal developmental issues.” ACOG goes on to say, “ACOG’s clinical guidance remains the same, and physicians should not change clinical practice until definitive prospective research is done. Most importantly, patients should not be frightened away from the many benefits of acetaminophen. However, as always, any medication taken during pregnancy should be used only as needed, in moderation, and after the pregnant patient has consulted with their doctor.”

Weighing the Risks and Benefits of Taking a Fever Reducing Medication

You should not take any medication without first running it by your doctor or midwife. You can weigh the risks and benefits of the fever and the over-the-counter medication to help you decide. This is also a great conversation to have with your doctor or midwife. You should consider other symptoms present to understand better why you have a fever and how to treat the underlying cause. The temperature, duration, and frequency of fevers may also play a role in your decision to use medication to reduce it. These decisions are not always cut and dry, and often there is a lot of gray areas. This is one of the reasons it is so crucial for you to have a doctor or midwife that you respect and trust. They are your trusted partner throughout your prenatal care and birth. If you have questions about the recommendations they give you, please ask. 

Talking to Your Doctor or Midwife

This podcast is not intended to be medical advice.  I intend to help get you more information and tools to add to your toolbox and help you make informed decisions. If you get a fever, please consult your doctor or midwife and discuss any medications before taking them.

Thank you to the amazing companies that have supported this episode.

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