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

When you’re pregnant, every pill, supplement, or over-the-counter remedy feels like a gamble. You want to feel better, but you’re terrified of hurting your baby. The truth isn’t black and white - but it’s not as scary as the internet makes it seem. About 2-3% of birth defects are linked to medications taken during pregnancy. That means for every 100 babies born with a defect, only 2 or 3 have a connection to a drug. The rest come from genetics, environment, or unknown causes.

What Exactly Is a Teratogen?

A teratogen is any substance that can interfere with fetal development and cause birth defects. It’s not just about illegal drugs or dangerous chemicals. Even common prescriptions and OTC meds can be teratogenic if taken at the wrong time or in the wrong dose. The most famous example? Thalidomide. In the late 1950s, this sleeping pill caused severe limb deformities in about 10,000 babies worldwide before being pulled from shelves. That tragedy changed how we test drugs for pregnancy safety - forever.

When You’re Most at Risk

The first trimester - weeks 1 to 12 - is the most dangerous window. That’s when your baby’s organs are forming. Between days 15 and 60 after conception, even a small exposure can cause major problems like heart defects, cleft palate, or missing limbs. After week 12, the risk of structural damage drops, but it doesn’t disappear. In the second trimester, medications might affect brain development or cause hearing loss. In the third trimester, the biggest risks are withdrawal symptoms, low birth weight, or problems with how organs function after birth.

Medications With Proven Risks

Some drugs are known dangers. If you’re taking one of these, don’t panic - but do talk to your doctor right away.

• Warfarin: Can cause fetal warfarin syndrome - a mix of facial deformities, bone problems, and intellectual disability. Risk is highest in the first trimester.
• Methotrexate: Used for cancer and autoimmune diseases, it blocks folate, which your baby needs to build a healthy spine. Increases neural tube defect risk by 10-20%.
• Carbamazepine: An epilepsy drug linked to a 1% chance of spina bifida and bleeding issues in newborns due to low vitamin K.
• Factor Xa inhibitors (rivaroxaban, apixaban): These blood thinners cross the placenta. There’s no antidote if bleeding happens. Avoid them entirely.
• Cannabis (THC): Increases risk of preterm birth, low birth weight, and stillbirth. THC stays in breastmilk for up to six days and may affect your baby’s attention and learning later on.

The Acetaminophen Debate

This is where things get messy. Acetaminophen (also called paracetamol) is the go-to painkiller for pregnant women. It’s in Tylenol, Excedrin, and hundreds of cold medicines. For years, doctors said it was safe. Now, some studies suggest a possible link to autism and ADHD - especially with long-term, daily use.

Here’s the catch: no one has proven it causes these conditions. The CDC says “some studies show an association,” but stops short of saying it’s a cause. Meanwhile, the American College of Obstetricians and Gynecologists (ACOG) came out strongly in September 2025, saying: “The risks of untreated fever or pain are far greater than any theoretical risk from acetaminophen.”

Think about it: If you have a high fever during pregnancy, your baby’s risk of neural tube defects goes up by 20-30%. If you’re in constant pain, your stress hormones can affect fetal growth. So while we keep studying acetaminophen, most experts still say: use it when needed, at the lowest dose, for the shortest time. Don’t avoid it out of fear - but don’t take it daily without a reason.

Why So Much Uncertainty?

You might wonder: Why don’t we know more? Why aren’t there clear answers?

Because we can’t run clinical trials on pregnant women. It’s unethical. So almost all the data we have comes from watching what happens after the fact - looking at birth records, tracking moms who took meds, or studying animals. That’s why about 70-80% of medications lack solid pregnancy safety data. Even if a drug is labeled “safe,” it might just mean “we don’t have proof it’s harmful.”

The FDA changed the system in 2015 to fix this. Instead of silly letter categories (A, B, C, D, X), labels now give real narratives: “There are 12 case reports of heart defects...” or “Animal studies showed no risk, but human data is limited.” It’s better - but still confusing. Many doctors still use the old letters because they’re easier to remember.

What Should You Do?

You don’t need to become a pharmacologist. But you do need a plan.

• Before you get pregnant: Review every medication you take - prescriptions, supplements, even herbal teas. Talk to your OB or a pharmacist. Some meds can be swapped for safer ones before conception.
• If you’re already pregnant: Don’t stop anything cold turkey. Stopping seizure meds, antidepressants, or blood pressure drugs can be more dangerous than keeping them. Work with your team to adjust doses or switch if needed.
• When in doubt: Call MotherToBaby. They’re a free service run by teratology experts. They answer over 10,000 calls a year. Most questions are about acetaminophen, antidepressants, or nausea meds like Zofran.
• Don’t trust Google: One Reddit thread says Zofran causes birth defects. Another says it’s safe. The truth? The data is mixed. Only your doctor can weigh your personal risk.

Who’s Responsible?

It’s not just your job to be careful. Your healthcare team needs to be proactive. Nurses should ask about meds at every visit. Pharmacists should review your list. Your OB should know what you’re taking - even if you think it’s “just a vitamin.”

The best outcomes happen when there’s a team: doctor, pharmacist, nurse, and you. If you’re on antidepressants, your psychiatrist should talk to your OB. If you’re on insulin, your endocrinologist should know you’re pregnant. Communication saves lives.

What’s Changing Now?

The FDA is working on something called the Sentinel Initiative - tracking 10 million patient records to spot patterns in pregnancy medication use. By 2026, we’ll have way better real-world data. Researchers are also exploring pharmacogenomics - testing your genes to see how you metabolize drugs. That could mean personalized advice: “Your body breaks down this med slowly, so avoid it,” or “You’re fine with this dose.”

But here’s the hard part: Only 2-3% of maternal health research funding goes to medication safety. That’s out of sync with how many women take meds during pregnancy. About 90% of pregnant women take at least one drug. We need more science - not more fear.

Bottom Line

You’re not alone in worrying. Most women feel this way. But fear shouldn’t stop you from treating pain, fever, depression, or high blood pressure. The goal isn’t to avoid all meds - it’s to use the right ones, at the right time, in the right dose.

If you’re planning pregnancy, get your meds reviewed. If you’re already pregnant and took something before you knew, call your doctor. Most exposures don’t cause harm. And if you’re unsure? Talk to someone who knows - not a forum, not a blog, not a stranger on Instagram. Your health and your baby’s health depend on accurate, personalized advice - not guesswork.

Next Steps

If you’re trying to get pregnant: Schedule a preconception visit. Bring your pill bottle list. Ask: “Which of these do I need to stop or switch?” If you’re already pregnant: Don’t skip your next appointment. Tell your provider every medication you’ve taken - even if you think it’s harmless. If you’re unsure about a drug, call MotherToBaby at 1-866-626-6847. They’re free, confidential, and staffed by specialists.

The goal isn’t perfection. It’s awareness. You’re not a risk - you’re a person making informed choices. And that’s what matters most.