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

When you’re pregnant, every pill, drop, or supplement feels like a gamble. You didn’t sign up for this kind of stress. You just wanted to feel better - maybe ease a headache, calm nausea, or manage a chronic condition - but now you’re terrified that the medicine you took might hurt your baby. The truth? Most medications don’t cause birth defects. But some do. And knowing which ones, when, and why can make all the difference.

What Exactly Is a Teratogen?

A teratogen is any substance that can interfere with how a baby develops in the womb. It’s not just drugs - it’s also alcohol, certain infections, and even high fevers. But when we talk about medications, we’re looking at prescription pills, over-the-counter drugs, and even herbal products that cross the placenta and affect the growing fetus.

The most infamous example? Thalidomide. In the late 1950s, this sleep aid was given to pregnant women for morning sickness. By 1961, over 10,000 babies worldwide were born with missing or shortened limbs. That tragedy changed medicine forever. Today, every drug is scrutinized for fetal risk - but the system isn’t perfect.

When Does Risk Happen? Timing Matters More Than You Think

Not all stages of pregnancy carry the same risk. The first trimester - especially weeks 3 to 8 after conception - is when organs are forming. That’s the most dangerous window for teratogens. A drug taken during this time can cause major structural problems like heart defects, cleft palate, or missing limbs.

After week 12, the baby’s organs are mostly formed. Medications at this stage are less likely to cause physical deformities but can still affect how those organs work. For example, exposure to certain blood pressure drugs in the second or third trimester can reduce blood flow to the placenta, slowing the baby’s growth. Or, drugs like SSRIs taken late in pregnancy can lead to temporary withdrawal symptoms in newborns - jitteriness, feeding issues, breathing problems.

And here’s the thing: if you took a medication before you knew you were pregnant, don’t panic. Most exposures don’t cause harm. The body is designed to filter out a lot of what passes through. But it’s still smart to tell your doctor what you took, when, and how much.

Medications With Proven Risks

Some drugs are known to be dangerous during pregnancy. These aren’t guesses - they’re backed by years of data:

• Warfarin (a blood thinner): Can cause fetal warfarin syndrome - facial deformities, bone problems, eye damage, and developmental delays. Risk is highest between weeks 6 and 9.
• Methotrexate (used for cancer, rheumatoid arthritis, ectopic pregnancy): Blocks folate, which is critical for neural tube development. Increases risk of spina bifida and other defects by 10-20%.
• Carbamazepine (for epilepsy): Linked to a 1% chance of neural tube defects and can cause bleeding in newborns due to low vitamin K.
• ACE inhibitors and ARBs (for high blood pressure): Can cause kidney damage, low amniotic fluid, and even fetal death if taken after the first trimester.
• Isotretinoin (Accutane for acne): One of the most dangerous - causes severe brain, heart, and facial defects. Women on this drug must use two forms of birth control and test for pregnancy monthly.
• Factor Xa inhibitors (rivaroxaban, apixaban): No safe dose established. They cross the placenta, and there’s no antidote if bleeding happens.
• Cannabis (THC): Even if you think it’s “natural,” THC crosses the placenta. Linked to lower birth weight, preterm birth, and long-term issues like attention problems and learning delays. It stays in breastmilk for days.

The Acetaminophen Debate: Why Experts Disagree

Acetaminophen - or paracetamol - is the go-to pain reliever for pregnant women. It’s been used for decades. But now, some studies suggest a possible link to autism and ADHD when taken long-term during pregnancy.

The CDC says: “Some studies show an association.” That’s not proof. But it’s enough to make people nervous.

Meanwhile, the American College of Obstetricians and Gynecologists (ACOG) says: “The risks of untreated fever or pain are far greater.” A high fever during early pregnancy increases the chance of neural tube defects by 20-30%. Chronic pain can lead to depression, poor nutrition, and preterm birth.

ACOG’s 2025 update reaffirmed that acetaminophen remains the safest option for pain and fever in pregnancy. They argue that avoiding it because of uncertain risks could do more harm than good.

So what should you do? Use the lowest effective dose for the shortest time. Don’t take it daily unless you need to. And never self-medicate for chronic pain without talking to your provider.

Why So Little Is Known About Pregnancy Medications

You’d think we’d know everything by now. But here’s the hard truth: we don’t.

It’s unethical to test new drugs on pregnant women in clinical trials. That means over 95% of what we know comes from watching what happens after the fact - case reports, registries, or animal studies. And animal results don’t always match humans.

Only about 2-3% of all research funding for maternal health goes to studying medication safety. Meanwhile, 70-80% of medications used in pregnancy have no solid safety data. That’s not a failure of science - it’s a failure of investment.

That’s why you’ll see conflicting advice online. One site says “safe,” another says “avoid.” The truth? It’s complicated. And that’s why you need a professional.

What You Can Do Right Now

You don’t need to guess. Here’s what works:

1. Review all meds before you get pregnant. Even if you’re not trying, use birth control if you’re on something risky. Many pregnancies are unplanned - nearly half in the U.S.
2. Don’t stop meds without talking to your doctor. If you have epilepsy, depression, or high blood pressure, stopping your drug could be more dangerous than keeping it.
3. Use trusted resources. MotherToBaby (run by experts in teratology) offers free, confidential advice. LactMed and the FDA’s pregnancy labeling are reliable too.
4. Ask your pharmacist. Pharmacists are medication experts. They know interactions, alternatives, and what’s safest.
5. Check labels. The FDA’s Pregnancy and Lactation Labeling Rule (PLLR) replaced the old A-B-C-D-X categories. Now, labels give real details: risks, data sources, clinical advice. Read them.

What About Supplements and Herbal Products?

Just because something is “natural” doesn’t mean it’s safe. St. John’s Wort can interfere with antidepressants. Black cohosh may trigger contractions. High-dose vitamin A (over 10,000 IU/day) causes birth defects. Even some prenatal vitamins have too much retinol.

Always tell your provider what supplements you’re taking - even if you think they’re harmless.

What’s Changing? The Future of Pregnancy Medication Safety

There’s hope. The FDA’s Sentinel Initiative is tracking 10 million patient records to find real-world patterns in medication use during pregnancy. By 2026, we’ll have better data than ever.

Researchers are also exploring pharmacogenomics - using your genes to predict how you’ll respond to a drug. That could one day tell you if a certain antidepressant is safe for you, based on your DNA.

But until then, the best tool you have is information - and a trusted care team.

Final Thought: You’re Not Alone

You’re not the only one stressing over this. Thousands of women every year wonder if that cold medicine, that migraine pill, that anxiety med might have hurt their baby. And many of them feel guilty, even when they did everything right.

The goal isn’t perfection. It’s awareness. It’s asking questions. It’s trusting your provider - not Google, not Reddit, not your well-meaning aunt.

You’re doing the best you can. And that’s enough.