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 take a pain reliever for a headache, and suddenly you’re wondering: could this hurt my baby? You’re not alone. Nearly 90% of pregnant women take at least one medication during pregnancy - from prenatal vitamins to antidepressants, from heartburn pills to cold medicine. But here’s the hard truth: not all medications are safe. Some can cross the placenta and interfere with your baby’s development, leading to birth defects, developmental delays, or even pregnancy loss.

What Exactly Are Teratogenic Medications?

Teratogenic medications are drugs that can cause physical or functional abnormalities in a developing fetus. The term comes from teras, the Greek word for monster - a grim reminder of the thalidomide disaster in the 1950s and 60s, when a popular sleep aid caused thousands of babies to be born with missing or stunted limbs. That tragedy changed medicine forever. Today, we know that certain drugs can disrupt the delicate process of fetal development, especially during the first trimester when organs are forming.

It’s not just the obvious ones. Even common over-the-counter drugs can carry risks. The key isn’t avoiding all medications - it’s understanding which ones are dangerous, when they’re most harmful, and what the alternatives are.

When Does the Risk Happen?

Timing matters more than you think. The first trimester - weeks 1 through 12 - is the most critical. That’s when your baby’s heart, brain, limbs, eyes, and ears are taking shape. Between days 15 and 60 after conception, the embryo is especially vulnerable. A medication taken during this window can cause major structural birth defects like cleft lip, heart defects, or missing fingers.

After week 12, the risk shifts. The baby’s organs are mostly formed, so major malformations are less likely. But medications can still cause problems: brain development, hearing, vision, or even behavior can be affected. In the third trimester, drugs might lead to withdrawal symptoms after birth - like jitteriness or breathing trouble - or alter how the baby’s liver and kidneys process toxins.

Some drugs don’t hurt the structure but mess with function. For example, high blood pressure meds that lower your blood pressure too much can reduce blood flow to the placenta, starving the baby of oxygen and nutrients. Others trigger contractions, leading to preterm labor.

Medications With Proven Teratogenic Risks

Not all drugs are created equal. Here are some with clear, documented risks:

• Warfarin: Used for blood clots, it can cause fetal warfarin syndrome - a mix of facial deformities, bone problems, and severe intellectual disability. Risk is highest in the first trimester.
• Methotrexate: A drug for autoimmune diseases and cancer, it blocks folate, a vitamin critical for neural tube development. Exposure in early pregnancy raises neural tube defect risk by 10-20%.
• Carbamazepine: An epilepsy medication linked to a 1% risk of spina bifida and other neural tube defects. It also lowers vitamin K, increasing bleeding risk in newborns.
• Factor Xa inhibitors (rivaroxaban, apixaban, edoxaban): These blood thinners cross the placenta easily. There’s no antidote if bleeding happens. Avoid them entirely during pregnancy.
• Cannabis (THC): Even if you think it’s natural, THC crosses into the baby’s bloodstream. It’s tied to low birth weight, preterm birth, and stillbirth. THC stays in breastmilk for days and may affect brain development.

These aren’t hypothetical risks. They’re backed by decades of clinical data. If you’re on any of these, don’t stop cold turkey - talk to your doctor. Uncontrolled seizures, blood clots, or mental illness can be just as dangerous as the medication.

The Acetaminophen Controversy

No drug has sparked more confusion than acetaminophen (Tylenol). It’s the go-to for fever and pain during pregnancy. But in recent years, some studies have linked long-term use to higher risks of ADHD and autism in children. The CDC says these associations exist - but they haven’t proven cause and effect.

Meanwhile, the American College of Obstetricians and Gynecologists (ACOG) came out strongly in September 2025, saying: "The conditions we treat with acetaminophen - fever, pain - are far more dangerous than any theoretical risk." Untreated fever during early pregnancy can raise neural tube defect risk by 20-30%. So ACOG stands by acetaminophen as the safest option for pain and fever control.

Here’s the bottom line: occasional use for a headache or fever is fine. Daily use for weeks on end? That’s where concern grows. Don’t panic if you took it early on. But if you’re using it constantly, talk to your provider about alternatives or underlying causes.

Why So Much Uncertainty?

You might wonder: why don’t we know more? The answer is simple - and heartbreaking. We can’t run controlled drug trials on pregnant women. It’s unethical. So nearly all our data comes from watching what happens after the fact: case reports, birth defect registries, and population studies. That means we often see patterns, but not proof.

Also, 70-80% of medications on the market have no solid pregnancy safety data. The FDA stopped using the old A, B, C, D, X categories in 2015 because they were too simplistic. Now labels give detailed narratives - but many doctors still rely on the old system, and patients are left confused.

Even online sources are unreliable. One mom on Reddit said she was told Zofran was safe for morning sickness by her OB, then read online it might cause heart defects. That kind of contradiction causes real anxiety. And anxiety itself? That’s bad for pregnancy too.

What Should You Do?

You don’t need to live in fear. You need a plan.

• Before you get pregnant: Review every medication - prescription, OTC, herbal, supplement - with your doctor. Switch to safer options if possible.
• If you’re already pregnant: Don’t stop anything without talking to your provider. Abruptly stopping seizure meds, antidepressants, or blood pressure drugs can be more dangerous than the drug itself.
• Use trusted resources: MotherToBaby (run by teratology experts) and LactMed (from the NIH) are free, science-backed sources. Avoid random blogs or Facebook groups.
• Consult a pharmacist: They’re trained in drug interactions and pregnancy risks. Many OBs don’t have time to dig into pharmacology - pharmacists do.
• Track everything: Write down every medication, dose, and date you took it. If something goes wrong, that record could save your baby’s future.

And if you took a medication before you knew you were pregnant? Don’t panic. Most exposures don’t cause harm. The risk is often low - and sometimes nonexistent. The best thing you can do now is get into prenatal care and let your provider know what you took.

The Bigger Picture

Pregnancy medication safety isn’t just about individual choices. It’s about systemic gaps. Only 2-3% of maternal health research funding goes to studying how drugs affect fetuses. Meanwhile, over 50 pregnancy registries exist to track exposures - but only 15-20% of women enroll. We’re flying blind in many ways.

But change is coming. The FDA’s Sentinel Initiative is now tracking 10 million electronic health records to find patterns in real time. Pharmacogenomics - testing how your genes affect drug response - could soon let doctors predict if a medication is risky for you specifically, not just in general.

For now, the message is clear: medication use in pregnancy requires careful thought, not fear. You’re not a risk-taker for taking what you need. You’re a caregiver making the best decision with the information you have.

What’s Next?

If you’re planning a pregnancy, schedule a preconception visit. Bring your pill bottles, supplements, and a list of conditions you treat. If you’re already pregnant, don’t wait for your next appointment - call your provider today. Ask: "Is this medication still safe for me now?" and "What’s the safest way to manage my condition?"

You’re not alone in this. Millions of women have walked this path. The goal isn’t perfection - it’s awareness. With the right information and support, you can protect both your health and your baby’s future.