Pregnancy and Medications: What You Need to Know About Teratogenic Risks and Birth Defects

When you’re pregnant, every pill, drop, or patch feels like a gamble. You take something to ease a headache, manage nausea, or control a chronic condition-and suddenly, you’re wondering: could this hurt my baby? The fear isn’t irrational. Around 2-3% of birth defects are linked to medications taken during pregnancy. That number might sound small, but for the families affected, it’s everything.

What Exactly Is a Teratogen?

A teratogen is any substance-medication, chemical, infection, or even radiation-that can interfere with fetal development and cause birth defects. Not all drugs are teratogens. In fact, most medications you take during pregnancy don’t cause harm. But some do, and the risk isn’t the same at every stage.

The first trimester is the most sensitive window. Between weeks 3 and 8 after conception, your baby’s organs are forming. That’s when exposure to certain drugs can lead to major structural problems-like missing limbs, heart defects, or neural tube defects. After week 12, the risk shifts. Instead of changing the shape of organs, drugs might affect how they function-leading to issues like low birth weight, developmental delays, or withdrawal symptoms after birth.

Medications with Proven Risks

Some drugs are known dangers during pregnancy. These aren’t hypothetical risks-they’re backed by decades of data.

• Warfarin (a blood thinner): Can cause fetal warfarin syndrome, which includes underdeveloped noses, bone problems, eye damage, and intellectual disabilities. The risk is highest in the first trimester.
• Methotrexate (used for cancer, autoimmune diseases): A folate blocker that increases neural tube defect risk by 10-20%. It’s absolutely not safe in early pregnancy.
• Carbamazepine (for epilepsy): Carries a 1% risk of spina bifida and can cause bleeding in newborns due to vitamin K deficiency.
• Factor Xa inhibitors (rivaroxaban, apixaban): These newer blood thinners cross the placenta. There’s no antidote if bleeding happens, and human safety data is extremely limited.
• Cannabis (THC): Linked to a 15-20% higher chance of low birth weight, 10-15% higher risk of preterm birth, and possible long-term effects like attention problems and lower IQ scores. THC stays in breastmilk for up to six days after use.

These aren’t rare cases. They’re well-documented outcomes. If you’re on any of these medications and planning pregnancy-or already pregnant-talk to your doctor immediately. Don’t stop cold turkey, but don’t wait either. A safe alternative often exists.

The Acetaminophen Debate

No drug has sparked more confusion than acetaminophen (paracetamol). It’s in Tylenol, Excedrin, and countless cold remedies. For years, it was the go-to pain reliever for pregnant women because it was considered safe.

Now, things are messy. Some studies suggest a link between long-term acetaminophen use and higher risks of ADHD or autism in children. The CDC mentions this as a potential concern. But here’s the other side: the American College of Obstetricians and Gynecologists (ACOG) issued a clear statement in September 2025 saying not treating fever or pain is far more dangerous.

Why? Because untreated fever during early pregnancy increases the risk of neural tube defects by 20-30%. Uncontrolled pain can raise stress hormones, which may affect fetal development too. ACOG’s position is simple: if you need acetaminophen, use it. The benefits outweigh the unproven risks.

This isn’t a contradiction-it’s context. One study doesn’t prove causation. But a mother’s untreated illness can be deadly. The key is using the lowest effective dose for the shortest time. Don’t take it daily for weeks without a reason. But don’t suffer through migraines or fevers either.

How Pregnancy Risk Labels Changed

You might remember the old A, B, C, D, X labels on medicine bottles. Those are gone. In 2015, the FDA replaced them with the Pregnancy and Lactation Labeling Rule (PLLR). Now, drug labels include detailed sections: risks, clinical considerations, and data sources.

Why the change? Because “Category D” didn’t tell you if the risk was 1% or 30%. It didn’t say whether the danger was in week 5 or week 25. The new labels give you real information: “In animal studies, this drug caused heart defects at high doses. In 200 human pregnancies, no birth defects were reported.”

But here’s the catch: about 70-80% of medications still lack solid data on pregnancy safety. That’s because testing drugs on pregnant women is ethically impossible. Most of what we know comes from accidental exposures, case reports, or animal studies. So even if a drug doesn’t have a clear warning, it doesn’t mean it’s proven safe.

What You Should Do Before and During Pregnancy

You don’t have to guess. There’s a system to help you.

1. Before you get pregnant: Review every medication you take-prescription, over-the-counter, supplements, herbs-with your doctor or pharmacist. Some medications need to be switched months in advance. For example, if you’re on isotretinoin (Accutane) for acne, you must stop at least one month before trying to conceive.
2. When you’re pregnant: Never start a new medication without checking with your provider. Even “natural” remedies like St. John’s Wort or high-dose vitamin A can be risky.
3. For chronic conditions: Don’t stop your meds because you’re scared. If you have epilepsy, high blood pressure, or depression, stopping your treatment can be more dangerous than the drug itself. Your doctor can often switch you to a safer version.
4. Use trusted resources: MotherToBaby (a service run by teratology experts) offers free, science-based advice. LactMed (from the NIH) tells you about drugs and breastfeeding. Don’t rely on Google or Reddit.

More than 90% of pregnant women take at least one medication. That’s normal. The goal isn’t to be drug-free-it’s to be informed. The right medication, at the right time, can save your life and your baby’s.

Why Confusion Is So Common

You’re not alone if you feel lost. One Reddit user wrote: “My OB said Zofran was fine for morning sickness. Then I read online it might cause birth defects. I cried for days.”

That’s the problem. Online forums mix truth with fear. A single case report gets turned into a headline. A 2018 mouse study becomes “Proven to cause autism.” Meanwhile, experts at MotherToBaby handle over 10,000 calls a year-mostly about acetaminophen, antidepressants, and anti-nausea drugs. The top concern? Contradictory advice.

Here’s the reality: science moves slowly. What we know today might change tomorrow. But that doesn’t mean you should panic. It means you need a guide. Your OB, your pharmacist, your midwife-they’re your team. Use them.

What’s Next for Pregnancy Medication Safety

The future is getting better. The FDA’s Sentinel Initiative is tracking 10 million patient records to find patterns in real-world use. Researchers are starting to use genetic testing to predict who might be more sensitive to certain drugs. Within five years, we may be able to say: “Based on your genes, this medication is low-risk for you.”

But right now, the biggest barrier isn’t science-it’s funding. Less than 3% of maternal health research money goes to studying medications. That’s why so many drugs are still in the “unknown” zone.

For now, the best tools you have are awareness and communication. Know what you’re taking. Ask why. Ask about alternatives. Ask what happens if you don’t take it.

You’re not just protecting your baby. You’re protecting yourself. And that’s the most important thing of all.

What to Do Next

If you’re planning pregnancy: schedule a medication review with your doctor or pharmacist. Bring a list of everything you take-even vitamins and herbal teas.

If you’re already pregnant: don’t stop or start anything without talking to your provider. Keep a log of every medication you use, including when and why.

If you’re unsure: call MotherToBaby at 1-866-626-6847. They’re free, confidential, and staffed by specialists who know exactly what you’re going through.

You don’t have to navigate this alone. The right information, at the right time, makes all the difference.