Pregnancy Registries: What We’re Learning About Medication Safety

When a woman finds out she’s pregnant, one of the first questions she might ask her doctor is: Is this medication still safe? Whether it’s an antidepressant, a seizure medicine, or a biologic for rheumatoid arthritis, millions of pregnant women take prescription drugs every year. But here’s the problem: most drugs aren’t tested on pregnant women before they hit the market. That’s where pregnancy registries come in-not as quick answers, but as the quiet, persistent effort to find real answers over time.

Why Pregnancy Registries Exist

The thalidomide disaster of the 1960s changed everything. Babies were born with severe limb defects because their mothers took a drug thought to be safe. After that, regulators realized they couldn’t wait for harm to show up in the population. They needed a system to watch for risks as soon as new drugs were used by real people-especially pregnant ones.

Pregnancy registries were built to fill that gap. They’re not clinical trials. They don’t assign drugs or test doses. Instead, they track women who are already taking a medication while pregnant, then follow them and their babies over months or even years. The goal? To spot patterns. Is there a higher rate of heart defects in babies whose moms took Drug X? Are there more preterm births with Drug Y?

The U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) now require these registries for many new drugs, especially biologics and treatments for chronic conditions. Why? Because pre-approval studies almost never include pregnant women. Ethical concerns, legal risks, and the complexity of pregnancy make it nearly impossible to test drugs on them before approval. Registries are the best tool we have to catch problems after the fact.

How They Work: From Exposure to Outcome

Imagine a woman takes her antidepressant daily. She finds out she’s pregnant. Her doctor mentions a registry for that medication. She signs up. That’s the start.

From there, registry staff collect detailed information: exactly which drug, what dose, when she started it, whether she took anything else, her medical history, smoking habits, even her stress levels. Then they track her pregnancy: Did she have a miscarriage? Was the baby born early? Was there a cleft lip or a heart defect? After birth, some registries follow the child for up to a year, checking for developmental delays or behavioral issues.

Unlike passive systems that rely on doctors reporting bad events, registries actively reach out. They call participants. They review medical records. They ask the same questions of every woman, reducing guesswork and memory errors. This is called prospective data collection-and it’s what makes registries more reliable than looking back at insurance claims or hospital records after the fact.

For example, the National Pregnancy Registry for Psychiatric Medications, run by Massachusetts General Hospital, has followed over 2,000 pregnancies since 2007. It tracks 45 different drugs, from SSRIs to lithium. Their data helped show that while some antidepressants carry small risks, the overall rate of major birth defects wasn’t significantly higher than in the general population. That’s not a guarantee of safety-but it’s reassurance based on real data, not theory.

The Limits: Small Numbers, Big Questions

Here’s the hard truth: most pregnancy registries are small. The average registry enrolls between 50 and 500 women. For rare drugs-like those used for rare autoimmune diseases-getting even 100 participants can take years.

Why? Because participation is voluntary. Many women are scared. Others don’t want to be contacted repeatedly. Some don’t trust the system. Only about 15-20% of eligible women actually join, according to MotherToBaby’s reports. That means the data is skewed. The women who sign up are often more informed, more anxious, or more connected to healthcare providers. They’re not a random sample.

Statistical power is another hurdle. To detect a doubling of a rare birth defect (say, from 1 in 100 to 2 in 100), you need over 1,200 exposed pregnancies. Very few registries reach that number. That’s why registries can tell you if a drug is likely safe for major defects-but they can’t rule out small increases in risk. A drug might slightly raise the chance of a minor issue like a cleft palate, and a registry might miss it entirely.

Dr. Allen Mitchell, a leading expert in birth defect epidemiology, puts it simply: “Pregnancy registries can never definitively establish safety. But they can give reassurance that a drug doesn’t carry a high risk for severe birth defects.” That’s a big difference.

What We’ve Learned So Far

Over the past 20 years, registries have changed how we think about pregnancy and medication.

For antiepileptic drugs, registries helped identify that valproate carries a high risk of neural tube defects and developmental delays-so now it’s avoided in women of childbearing age unless absolutely necessary. For SSRIs like sertraline and citalopram, data showed no clear link to major structural birth defects, helping many women continue treatment without fear.

Biologics used for conditions like Crohn’s disease or psoriasis were once a mystery. Now, registries have shown that drugs like adalimumab and infliximab cross the placenta, but don’t appear to increase the risk of birth defects. That’s allowed doctors to recommend continuing treatment during pregnancy for women whose health depends on it.

Psychiatric medications remain the most studied group. Over a dozen registries exist just for antidepressants, antipsychotics, and mood stabilizers. The data is still incomplete, but it’s growing. One key finding: stopping medication during pregnancy often carries greater risks than continuing it-for both mother and baby. Depression and anxiety during pregnancy are linked to preterm birth, low birth weight, and postpartum complications. Registries help balance those risks.

What’s Changing Now

The system isn’t perfect-but it’s getting better.

In 2022, the FDA launched the Pregnancy Safety Research Network to connect all the separate registries into one coordinated system. Instead of 80+ isolated studies, they’re now sharing data, standardizing how they collect information, and pooling numbers to increase statistical power.

New methods are being tested too. Some registries now link directly to electronic health records, pulling in lab results, doctor visits, and medication fills automatically. Others are adding control groups-women with the same illness who didn’t take the drug-so researchers can tell if the problem is the medicine or the disease itself.

The International Society of Pharmacoepidemiology updated its guidelines in 2023 to stress this: you can’t just compare exposed babies to the general population. You have to compare them to women with the same underlying condition who didn’t take the drug. Otherwise, you might blame the medicine for problems caused by the illness.

And the scope is expanding. In January 2024, the National Pregnancy Registry for Psychiatric Medications added 18 new drugs, including newer antidepressants and atypical antipsychotics. That’s over 45 medications now under active study.

What Women Experience

Behind every data point is a person.

Women who join registries often say they feel less alone. They get regular updates. They’re not left guessing. One mother, taking lamotrigine for epilepsy, told her registry counselor: “I didn’t want to be the one who found out too late that my baby was affected because no one was watching.”

But it’s not easy. Some women feel guilty for taking medication. Others are frustrated when they ask, “Is this safe?” and the registry staff can’t give a yes-or-no answer. The data isn’t ready yet. It takes years.

MotherToBaby, which runs several U.S. registries, found that 78% of participants felt satisfied with their experience. They liked knowing they were helping future moms. But recruitment remains a struggle. Many doctors don’t mention registries. Some assume women won’t want to join. Others don’t know how to explain them.

The Bigger Picture

Pregnancy registries aren’t the whole solution. They’re one piece of a larger puzzle. Database studies using insurance records can catch more cases, but they lack detail. Case-control studies are fast but rely on memory. Registries are slow, expensive, and small-but they’re the most accurate tool we have for direct, real-world observation.

Experts like Dr. Sonia Hernandez-Diaz argue we need a tiered approach: use registries to spot signals, then use big data to confirm them. That’s exactly what’s starting to happen. The FDA now encourages combining registry data with claims databases to get the best of both worlds.

The cost? Around $500,000 to $2 million per registry per year. Pharmaceutical companies pay for most of it, as required by regulators. But without them, these studies wouldn’t exist.

Right now, over 80 active registries operate in the U.S., with about 30 new ones starting each year. The global market for pregnancy safety monitoring is growing fast-projected to hit $500 million by 2030. That’s not just business. It’s public health.

What You Should Know

If you’re pregnant and taking medication:

• Ask your doctor if there’s a registry for your drug. You can also check MotherToBaby.org or the FDA’s website.
• Participation is voluntary. No one will pressure you.
• Joining doesn’t mean you’re a guinea pig. You’re helping science-and possibly helping another woman down the line.
• Don’t expect immediate answers. Registries take time.
• Stopping your medication without medical advice can be riskier than continuing it.

Registries won’t tell you every possible risk. But they’re slowly replacing fear with facts. And for pregnant women, that’s everything.