Acetaminophen and NSAIDs in Pregnancy: What You Need to Know by Trimester

When you're pregnant and dealing with a headache, fever, or back pain, the last thing you want is to guess whether your medicine is safe. You’re not just thinking about yourself anymore-you’re thinking about your baby. That’s why so many people avoid all pain relievers during pregnancy, even when they really need them. But here’s the truth: acetaminophen is still the safest option for most pregnant people, and NSAIDs like ibuprofen and naproxen carry real risks that change depending on how far along you are.

What Acetaminophen Does (and Doesn’t Do) in Pregnancy

Acetaminophen, also known as paracetamol, has been used by pregnant people since the 1950s. It works to reduce pain and fever without affecting blood clotting or inflammation like NSAIDs do. That’s important because inflammation and fever themselves can be dangerous during pregnancy. A fever over 102°F in the first trimester has been linked to a 2.3 times higher risk of neural tube defects, according to a 2017 study in Birth Defects Research. Untreated fever also raises the chance of miscarriage by 1.5 times.

Large studies involving tens of thousands of pregnancies have found no increased risk of birth defects, preterm birth, or low birth weight from acetaminophen when used at standard doses: 325 to 1,000 mg every 4 to 6 hours, not exceeding 4,000 mg in 24 hours. A 2020 analysis from the National Institutes of Health (PMC2809170) reviewed data from over 5,000 pregnant women and found no pattern of harm.

Even concerns about autism or ADHD in children have been thoroughly studied. A 2023 JAMA Network Open study followed 97,006 mother-child pairs and found no meaningful link between acetaminophen use and neurodevelopmental outcomes. The adjusted odds ratio for autism was 1.03-essentially the same as if no medication was taken. The same study showed no increase in ADHD or intellectual disability risk.

So why the confusion? In 2021, a group of scientists published a theoretical warning in Nature Reviews Endocrinology suggesting acetaminophen might interfere with hormone systems. But no study has proven this leads to actual harm in babies. Major medical groups like the American College of Obstetricians and Gynecologists (ACOG), the Society for Maternal-Fetal Medicine, and the American Academy of Pediatrics all agree: acetaminophen is the best choice for pain and fever in pregnancy.

Why NSAIDs Are Risky After 20 Weeks

NSAIDs-like ibuprofen (Advil, Motrin), naproxen (Aleve), and diclofenac (Voltaren)-work differently. They block enzymes that cause inflammation, pain, and fever. But they also block prostaglandins that help maintain blood flow to the baby’s kidneys and keep a key blood vessel (the ductus arteriosus) open.

Before 20 weeks, NSAIDs are generally considered low risk. But after that point, things change fast. The FDA updated its guidance on October 15, 2020, and now says: avoid NSAIDs at 20 weeks or later. Why? Because within 48 to 72 hours of exposure, NSAIDs can cause the baby’s kidneys to produce less urine. That leads to low amniotic fluid-called oligohydramnios. Studies show this happens in 1 to 2% of cases after 20 weeks, compared to just 0.1% in unexposed pregnancies.

Low amniotic fluid can compress the baby’s lungs and limbs, affect growth, and even lead to stillbirth in rare cases. If you’ve taken an NSAID after 20 weeks and your doctor finds low fluid on ultrasound, they’ll tell you to stop immediately. In most cases, fluid levels bounce back within days after stopping the drug.

After 30 weeks, there’s another risk: premature closure of the ductus arteriosus. This blood vessel normally closes right after birth, but if it closes too early, it can strain the baby’s heart and cause pulmonary hypertension. The risk is small-about 0.5 to 1%-but serious enough that doctors now treat NSAIDs like a time bomb after 20 weeks.

And here’s the tricky part: many cold and flu meds contain NSAIDs. One in three over-the-counter products includes ibuprofen or naproxen, often hidden under names like "sinus relief" or "full-spectrum pain relief." Always check the Drug Facts label. If you see "ibuprofen," "naproxen," or "NSAID," put it back.

What About Aspirin?

Low-dose aspirin (81 mg) is an exception. It’s commonly prescribed during pregnancy to prevent preeclampsia in high-risk people. That’s different from taking regular-strength aspirin for a headache. The FDA’s warning about NSAIDs doesn’t apply to low-dose aspirin when used under medical supervision. If your doctor gave you baby aspirin, keep taking it as directed.

Real-World Confusion: Why So Many People Are Scared

Despite clear guidelines, many pregnant people avoid acetaminophen altogether. A 2023 survey by the American Academy of Family Physicians found that 68% of pregnant patients avoid all pain medication because they’re afraid. And 42% of them specifically avoid acetaminophen because of social media posts claiming it causes autism.

Dr. Magloire, a family doctor in Minnesota, says: "I never recommend NSAIDs during any trimester because patients don’t always know how far along they are." That’s true for many. Some people don’t realize they’re pregnant until they’re 8 or 10 weeks along. Others forget their last period. So even if you’re told NSAIDs are "okay before 30 weeks," it’s easy to misjudge your timeline.

Reddit threads from r/BabyBumps and r/ObGyn in early 2024 show the same pattern: people stopping acetaminophen after reading a single article about "possible" autism links. But correlation isn’t causation. Just because some children with autism had mothers who took acetaminophen doesn’t mean the medicine caused it. The science doesn’t support that link.

How to Use Acetaminophen Safely

If you need acetaminophen, here’s how to use it right:

1. Start with the lowest dose that works-usually 500 mg.
2. Take it only when you need it. Don’t use it daily unless your doctor says so.
3. Don’t take it for more than 3 to 5 days in a row without checking in with your provider.
4. Check all medicine labels. Some cold, flu, and sleep aids contain acetaminophen too. Don’t double up.
5. If you’re taking other meds, ask your pharmacist or doctor if they interact with acetaminophen.

There’s no need to suffer through pain or fever. Untreated symptoms can harm both you and your baby more than acetaminophen ever could.

What If You Took NSAIDs After 20 Weeks?

If you accidentally took an NSAID after 20 weeks, don’t panic. One or two doses are unlikely to cause harm. But tell your provider. They may recommend an ultrasound to check your amniotic fluid levels. If fluid is low, they’ll monitor you closely and likely advise you to avoid NSAIDs for the rest of your pregnancy.

If you’ve been taking NSAIDs regularly-say, for chronic back pain-your provider may suggest switching to acetaminophen or exploring non-drug options like physical therapy, heat packs, or prenatal yoga.

What’s Changing in 2025?

The FDA is still reviewing acetaminophen labeling, especially around long-term use. A 2025 notice acknowledged that some studies suggest "the risk may be most pronounced when acetaminophen is taken chronically throughout pregnancy." But they also emphasized: "The benefits outweigh the theoretical risks."

The NIH is now running the Acetaminophen Birth Cohort Study, tracking 10,000 children born to mothers who took acetaminophen during pregnancy. Results won’t be ready until 2027, but it’s the largest study of its kind. Meanwhile, ACOG reaffirmed its position in September 2025: "The conditions people use acetaminophen to treat during pregnancy are far more dangerous than any theoretical risks."

And here’s something new: research in 2024 found that 15% of pregnant people carry a gene variant (CYP2E1) that affects how their body processes acetaminophen. That means some people might need different doses. But since we can’t test for this routinely yet, sticking to standard dosing remains the safest advice.

Bottom Line: What to Do

For pain or fever during pregnancy:

• Use acetaminophen as needed, at the lowest effective dose, for the shortest time possible.
• Avoid NSAIDs (ibuprofen, naproxen, diclofenac) after 20 weeks.
• Check every medicine label-even "natural" or "herbal" remedies can be risky.
• Don’t let fear stop you from treating symptoms that could hurt you or your baby.

Acetaminophen isn’t perfect. But right now, it’s the best tool we have. And when used correctly, it keeps you and your baby safer than going without treatment.