3 Charts | Fevers May Increase Autism Risk | Visualized Science

Reviewed by The Clinical Committee

July 23, 2019

  • A new study suggests that fevers during pregnancy may increase the risk of autism.

  • Fevers in the 2nd trimester were associated with a 40% increase in autism risk.

  • Having multiple fevers after the 12th week of pregnancy were associated with a 3-fold increase in autism risk.

Fevers Linked to Autism Risk

Fevers Linked to Autism Risk

Figure 1: Fevers Linked to Autism Risk. Fevers during the second trimester of pregnancy were associated with a 40% increase in autism risk. Bars above are scaled to the odds of a baby developing autism. They are relative to mothers who did not have fevers during the second trimester. These data were obtained from a cohort of 95,754 mothers in Norway, in which 583 had babies diagnosed with autism.

Having a fever in the second trimester may increase the risk of autism.

A new prospective cohort study from Norway found that mothers who had a fever during the second trimester of pregnancy had a roughly 40% higher chance of having a child with autism.

Fevers in the first and third trimesters had little to no effect. This is consistent with the fact that fetuses go through stages of development. As the brain develops, they are most vulnerable to external risks at specific periods.

Previous studies had found evidence that infection and fever may play a role in autism risk. This is one of the first large-scale studies to provide statistical evidence of this effect.

Source: Prenatal fever and autism risk

How the Fever-Autism Link Works

How the Fever-Autism Link Works

Figure 2: How the Fever-Autism Link Works. Second-trimester fevers have been associated with higher autism risk. This is the proposed mechanism. Bacteria and viruses enter the body and cause an infection. This causes the immune system to release inflammatory compounds. These can enter the fetus’ brain during a critical development period

Researchers believe that this may be caused by inflammatory compounds released by the immune system.

When the body encounters viruses and bacteria, white blood cells release inflammatory molecules that signal the presence of potential germs. Since the mother and the fetus share a blood supply, these molecules can potentially affect the fetus if an infection happens during a particularly critical development period.

Top Questions and Answers

Source: Prenatal fever and autism risk

Multiple fevers are linked to a higher risk of autism

Multiple fevers are linked to a higher risk of autism

Figure 3: Multiple fevers are linked to a higher risk of autism. Multiple fevers after 12 weeks were associated with a higher risk of autism. Having 1-2 fevers after 12 weeks is associated with a roughly 30% higher risk of autism. Having 3 or more fevers after 12 weeks is associated with a 3.1x higher risk of autism.

The risk of autism goes up with the number of fevers a mother has after 12 weeks. Having 1-2 fevers was associated with a small increase in risk. Having three or more fevers was associated with around triple the risk of autism.

Given that this research is so new, there are still many unanswered questions about this effect. The most important unanswered question is whether this effect is causal. Do fevers actually cause autism or are they only correlated with something else that does?

These data point to a potentially concerning link. However, we will need more research before we know this for sure and before we know how to fully prevent this. In the meantime, here are two common-sense tips that we would recommend:

Our recommendations: 1-Take a Tylenol when you have a fever: There is some evidence that taking medication to reduce fever may reduce this effect.

2-Keep healthy: Reduce your stress, stay hydrated, and stay healthy. Whether fevers affect autism or not, self-care is always going to be a good thing.

Study Methods

Autism + Fever Study

Number of Patients


Study Type

Prospective Cohort

Exposure Studied

Fevers during pregnancy

Evidence Score:


Endpoints - Researchers used ASD diagnosis as an endpoint, which is appropriate for this type of study.


Study Size - The study size was large enough to find significant effects and differences between groups.


Study Type - Researchers used a prospective cohort study. Prospective cohort studies are good for studying potential links when clinical trials are not feasible. However, they do not confirm causation. We cannot say whether fevers cause a higher autism risk or whether this is just a correlation.

Expert Opinions

Centers for Disease Control

A study from the Centers for Disease Control and Prevention (CDC) found that women who had a cold or flu with fever just before or during early pregnancy may be more likely to have a baby born with a birth defect.

Centers for Disease Control

Women who reported having a fever just before or during early pregnancy were more than twice as likely to have a baby with a neural tube defect compared with women who did not report having a fever.

Scan J Pain

Acetaminophen is the safest medicine as analgesics for nociceptive pain and antipyretics in childhood and pregnancy. There is no alternative medication of acetaminophen. Acetaminophen should not be withheld from children or pregnant women for fears it might develop adverse effects. Acetaminophen should be used at the lowest effective dosage and for the shortest time.

Clearvue Health is not affiliated with above organizations. The information above is provided to highlight and link to useful further reading.

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