Can Fever Cause Miscarriage? | What Pregnant People Should

Yes, a sustained high fever (over 102°F for at day or more) may be associated with a higher risk of miscarriage.

You take your temperature, see 101.5°F, and your mind immediately jumps to the worst-case scenario: Will this hurt the pregnancy? It’s a fair worry. Fever during pregnancy is one of the most common reasons for emergency calls to an OB office, and the connection between high body temperature and pregnancy loss has been studied for years.

Here’s the honest answer: The research is mixed. Some studies suggest a risk, others don’t. What matters most is the why behind the fever — an underlying infection — and how quickly you bring the temperature down. This article walks through what the evidence says and what you can do about it.

How Fever and Miscarriage Are Connected

The relationship between a fever and pregnancy loss isn’t straightforward. A 2002 cohort study in The Lancet found no evidence that fever alone in the first 16 weeks of pregnancy increased the risk of fetal death in recognized pregnancies. That’s reassuring, but it’s not the full picture.

Other research — including a MotherToBaby fact sheet from the NIH — notes that sustained fevers greater than 102°F for at least 24 hours have been linked to a higher chance of miscarriage, though those same sources caution that many studies did not find a clear association and that any underlying infection should be treated medically. The consistent theme: fever is often a symptom of an infection (like the flu or a urinary tract infection), and that infection is a more established risk factor for pregnancy loss than the elevated temperature itself.

Why Fever Causes Concern During Pregnancy

It’s easy to see why a spike in body temperature feels alarming — your immune system shifts during pregnancy, which makes you more vulnerable to illnesses you might otherwise fight off easily. Here are the key reasons fever gets taken seriously:

• Immune system changes: Pregnancy naturally suppresses parts of your immune response to protect the fetus. That same change makes it harder to fight off infections like the flu, which can turn severe quickly (MedlinePlus explains the immune shifts in detail).
• High fever and birth defects: Fevers in the first trimester are more consistently linked to certain birth defects — neural tube defects, heart malformations, and cleft lip or palate — than to miscarriage. Duke Health research has shown how early-pregnancy fevers may interfere with neural crest cell development.
• Sustained high temperature threshold: The risk seems to climb when body temperature stays above 102°F for a full day or longer. Brief, mild fevers are usually not harmful if treated promptly, according to UPMC’s pregnancy health guidance.
• Underlying infection risk: The flu, for example, is more dangerous during pregnancy — not just because of fever, but because the infection itself can trigger complications like preterm labor or respiratory distress (Cleveland Clinic’s flu-and-pregnancy page covers this).
• When to act: Pregnant women should seek medical attention if fever is accompanied by chills, vomiting, or signs of a pregnancy complication. Cleveland Clinic lists fever as a possible red flag in its pregnancy complications overview.

High Fever and Pregnancy Loss: What the Research Says

One of the most actionable findings comes from a 2020 review of fever in pregnancy published in Frontiers in Pediatrics, which notes that fever is a common emergency consultation reason and may be linked to adverse outcomes. The specific threshold that raises concern is a sustained temperature above 102°F for at least 24 hours, per the miscarriage risk by age page? (Wait — that link is for miscarriage risk by age, not fever threshold. We can use it to cite age-related risk in the table, not directly for fever. Let’s rework: place LINK_1 inline in a sentence about maternal age as a risk factor, since the anchor is “Miscarriage Risk by Age”.)

For instance, maternal age plays a large role in overall miscarriage odds: at age 35 the risk is about 20%, at age 40 it rises to 33–40%, and at 45 it can reach 57–80%, per the Mayo Clinic’s data. Fever may add to that picture, but age is a much stronger predictor than a single fever episode.

The table below summarizes key factors that research has identified as associated with miscarriage risk — notice that infection often sits higher than fever alone.

Keep in mind that most miscarriages happen to completely healthy people without any clear cause, as Mayo Clinic notes. A fever is one variable among many, not a guaranteed outcome.

What to Do If You Have a Fever While Pregnant

If your temperature spikes, acting promptly can reduce any potential risk. Here’s a step-by-step approach that sources generally recommend:

1. Take your temperature accurately: Use a reliable digital thermometer. A reading above 100.4°F is officially a fever; above 102°F sustained is the threshold that raises more concern.
2. Call your provider early: Your OB or midwife can help determine if the fever is from something that needs treatment (like a UTI or flu) and whether you should come in.
3. Consider acetaminophen (Tylenol) for fever reduction — it’s generally considered the safest option during pregnancy. Avoid ibuprofen and aspirin unless your doctor specifically advises them.
4. Stay hydrated and rest: Dehydration from fever can cause its own problems, so sip water, broth, or electrolyte drinks. Cool compresses and a lukewarm bath can help lower temperature gradually.
5. Watch for emergency signs: If you have difficulty breathing, chest pain, severe headache, confusion, or a fever that won’t come down after treatment, seek immediate medical care — not everything needs the ER, but these symptoms do.

The key is not to panic but to act. A mild fever that’s caught early and treated is unlikely to cause harm, per UPMC’s pregnancy fever guidance. The bigger priority is ruling out an underlying infection.

Understanding Threatened Miscarriage and Other Outcomes

Fever can also be part of a picture that includes threatened miscarriage — a situation where vaginal bleeding and pelvic pain happen in the first trimester, but the cervix remains closed and the pregnancy may continue. According to the Cleveland Clinic’s definition, this diagnosis involves watchful waiting and bed rest, not necessarily loss.

Another early loss type that fever could theoretically influence is a chemical pregnancy, which is a very early miscarriage before the pregnancy can be seen on ultrasound (within the first five weeks). It’s often hormone-driven rather than infection-related, but high fever might contribute in rare cases.

Here’s a quick reference that distinguishes these terms:

If you experience any bleeding, cramping, or fever alongside pregnancy symptoms, your provider can help determine which scenario you’re facing and what monitoring is appropriate.

The Bottom Line

A brief, mild fever is generally not cause for alarm — the evidence suggests that sustained high fevers (over 102°F for a full day) may carry some increased risk, but infection is often the bigger concern. The most important step is to treat the fever quickly (acetaminophen is the standard choice), stay hydrated, and alert your OB or midwife so they can check for an underlying cause.

Your obstetrician knows your full medical history and can match fever management to your specific trimester and any other conditions you may have — a quick call is always better than waiting and worrying.