HCPs have dozens of possibilities to consider when pregnant women present with a fever, but usually start with common infections such as respiratory illness or urinary tract infection (depending on the presence of additional symptoms). If those are ruled out, HCPs can move to other less common, but potentially serious infections (listeria, salmonella, chorioamnionitis, sepsis, etc.).
Fever: a response to an underlying disease, usually an infection, that results in an elevated body temperature; not an illness itself, but a sign of illness.
Fever is relatively common during pregnancy, similar to the general population. One study of 24,000 pregnant women determined that 18.5% had experienced at least one fever within the first 16 weeks.
The American College of Critical Care Medicine, the International Statistical Classification of Diseases, and the Infectious Diseases Society of America define fever as a core temperature of 100.9° F (38.3° C) or higher, irrespective of the cause; other sources define it as 100.4° or higher.
Fever is a necessary part of the immune system, as long as it does not get too high or last too long. Extremely high fever is assessed to cause damage at the cellular level in almost every organ system within the body, and may be most evident at 105.8° F and higher. However, it is possible that a pregnant woman and her fetus could be more sensitive to fever’s effects at lower temperatures.
Concern over fever during pregnancy is related to research conducted on heat exposure (hyperthermia) and the negative effects it can have on a pregnancy.
Hyperthermia causes a wide range of structural and functional defects, and fever itself has also been associated with some of the same effects. High maternal fever for an extended period is therefore considered a human teratogen, but there are many aspects to consider.
First, it is necessary to take the underlying disease into account because fever is only a clinical symptom. Among the possible causes, infection is the most common, which is often caused by viral, bacterial, or fungal organisms. In general, fever usually represents more serious infections than illnesses without a fever.
It is currently assessed that adverse pregnancy-related outcomes associated with a fever could be due to the fever itself, the illness caused by the fever, or potentially the medications/treatments used to treat the fever or the illness.
The U.S. Centers for Disease Control and Prevention (CDC) indicates that fever is associated with numerous birth defects to include anencephaly, spina bifida, encephalocele, cleft lip, and cleft palate, as well as gastrointestinal and kidney disorders.
Evidence appears to the be the strongest for congenital heart defects and defects of the central nervous system, to include the neural tube.
Regarding miscarriage and fetal death, miscarriage risk remains inconsistent, and positive associations were found mostly in animal studies. Fetal death is even weaker, as several studies found no evidence that fever causes fetal death, while one found a slightly higher risk in women with higher fever for a prolonged period.
Developmental concerns (autism, attention-deficit/hyperactivity disorder) have also been inconsistent; some studies found a correlation, others found no correlation; some found a correlation but related it to the illness or medication and not the fever, and others found correlations that were specific to certain time frames of pregnancy.
Acetaminophen is also associated with developmental disorders; however, many pregnant women take acetaminophen for fever. This scenario is a current conundrum in the research community: when a woman has a fever, takes acetaminophen, and the baby is born with a physical or mental birth defect, is the fever responsible, is the acetaminophen responsible, is it a combination of both, or are other factors responsible?
Based on studies assessing risk of fever during pregnancy, fever appears to be more strongly associated with negative outcomes than either acetaminophen alone, or when acetaminophen was used with a fever.
Some researchers indicate that fever is the real teratogenic factor and acetaminophen may reduce the risk of certain negative outcomes, but overall, evidence remains inconsistent.
Regardless, fever and acetaminophen use are both common during pregnancy and not all babies born to mothers who experienced a fever or take acetaminophen during pregnancy develop a developmental disorder.
Learn more about acetaminophen, and why dozens of medical professionals called for better focused research on this medication during pregnancy (September 2021).
Variables to Consider
The consequences of fever depend on the extent of temperature elevation, its duration, the stage of pregnancy when it occurs, the illness causing the fever, and whether medication was used, at which dosage, and for how long. Studies that have accounted for all these variables are nonexistent.
Additionally, studies cannot be put together and analyzed as a whole because of how differently they are designed. Some studies assess for only one specific type of birth defect, while others looked at as many as 30 different types.
Further, it is not ethical to induce fever in a pregnant woman, and those surveyed who did experience pregnancy loss or a baby with a birth defect were more likely to recall fever than women who did not experience those outcomes.
Finally, acetaminophen has also been associated with ADHD and autism, but even those results are inconsistent, and some are methodologically flawed (for example, for some studies, women just answered “yes” or “no” to whether they took acetaminophen), and these studies have the same obstacles as those studying fever.
It is also possible that while fever may be a teratogen, it is only harmful when high, and it is possible that low-grade fevers do not pose the same level of risk.
For example, one study found birth defects in women who experienced fevers of 102° F (38.9° C) or higher for extended periods of time in the first month of pregnancy as well as stillbirth later in pregnancy, but did not find these associations in women who experienced a lower temperature. A threshold for damage beginning at 102° F has also been found in other studies.
However, the case for fever itself as a strong causal factor for complications is also seen in women who contract a fever during labor and delivery.
The prevalence of intrapartum (during labor) fever ranges from 1.6% to 14.6% of all deliveries.
Fever of 102° F or higher during labor has been associated with an extremely elevated risk for assisted delivery, neonatal sepsis, low Apgar scores, and neonatal intensive care unit admissions.
Fever is also assessed to increase the risk of neonatal encephalopathy, cerebral palsy, and neonatal death. While these complications are well-documented, it is not clear how fever leads to these outcomes, or how the above factors cause fever.
HCPs will monitor women to assess/manage a fever that occurs during labor. If the fever is thought to be the result of an intraamniotic infection, antibiotic treatment may be recommended. HCPs will confer with neonatal specialist teams and will discuss possible treatment and delivery options with the woman and her partner/support team.
Pregnant women should call their HCP anytime they have a fever during pregnancy. HCPs have many tools and options available to attempt to determine the cause of a fever during pregnancy.
Urinary tract infections and others types of infections can be detected through urine tests; blood work can also provide clues. Further, rapid office tests are available for influenza, strep throat, respiratory syncytial virus, and COVID-19* (*availability of these tests may change).
Women with very high fevers need to discuss with their HCP the risks and benefits of taking anti-fever medications for their fever, as the risks of a very high fever during pregnancy may outweigh any risks associated with these medications (read Acetaminophen).
To prevent infections of the lower genital tract that can also cause fever during pregnancy, women should learn to recognize the signs and symptoms of possible infection and call their HCP as soon as possible for earlier diagnosis and treatment (to prevent the infection from ascending). Read Vagina and Cervix for more information.
Women should also consider sharing and submitting their experience below if they had a fever during pregnancy. This can help other women learn additional perspectives regarding this concern.
Intrapartum Management of Intraamniotic Infection (American College of Obstetricians and Gynecologists)
10 Tips for Preventing Infections Before and During Pregnancy (U.S. Centers for Disease Control and Prevention)