Pregnancy Registries: What We’re Learning About Medication Safety

When a woman takes medication during pregnancy, no one knows for sure if it’s safe-not even her doctor. Clinical trials don’t include pregnant women, and animal studies don’t always predict what happens in humans. That’s why pregnancy registries exist: to fill the biggest gap in drug safety we’ve ever faced.

These aren’t just databases. They’re active, ongoing studies that follow women from the moment they start a medication through birth and sometimes beyond. The goal? To find out if a drug causes birth defects, preterm labor, low birth weight, or long-term developmental issues. And over the last decade, they’ve started giving us real answers-slowly, carefully, and one pregnancy at a time.

How Pregnancy Registries Work

Pregnancy registries don’t wait for problems to happen. They get in early. A woman finds out she’s pregnant while taking a medication-maybe for epilepsy, depression, or an autoimmune disease-and she’s offered a chance to join a registry. She consents. She answers questions about the drug, the dose, when she started it, whether she smoked or drank, and what other medications she’s on. Then, her healthcare providers report back on her pregnancy outcome: was it full-term? Was the baby healthy? Were there any physical abnormalities?

Unlike passive systems like the FDA’s Adverse Event Reporting System (FAERS), which rely on doctors or patients to report problems after they occur, registries proactively collect data before outcomes are known. This reduces guesswork and recall bias. If a woman forgets she took a pill at week 5, it’s not a problem-the registry asks her right away.

Some registries go even further. The National Pregnancy Registry for Psychiatric Medications, run by Massachusetts General Hospital, follows children for up to 12 months after birth to check for delays in motor skills, speech, or social development. That’s not something you can get from a hospital chart or insurance claim.

What We’ve Learned So Far

Registries have changed how we think about certain drugs. Take lamotrigine, a common anti-seizure medication. Before registries, many doctors avoided it in pregnancy because of theoretical risks. But data from the North American Antiepileptic Drug Pregnancy Registry showed no increased risk of major birth defects compared to the general population. Today, it’s one of the first-line choices for women with epilepsy who are pregnant.

Same with SSRIs like sertraline. Early studies suggested a link to heart defects, but registry data from over 1,500 pregnancies showed no consistent pattern. The risk, if any, is small-smaller than the risk of untreated depression. That’s huge. It means women can now make informed choices instead of being told to stop their medication cold.

For newer biologic drugs-like those used for rheumatoid arthritis or psoriasis-registries are often the only source of human data. Drugs like adalimumab and etanercept were once avoided entirely during pregnancy. Now, registry data from over 2,000 pregnancies show no clear signal of birth defects. That’s not proof of safety, but it’s enough reassurance for many doctors and patients to proceed.

The Limits of the Data

Here’s the hard truth: registries can’t prove a drug is completely safe. They can only say it doesn’t cause major defects at a higher rate than expected.

Why? Sample size. Most registries enroll between 50 and 500 women. To detect a doubling of a rare defect-say, from 1 in 100 to 2 in 100-you’d need over 1,200 exposed pregnancies. Very few registries reach that number. And if a drug is only taken by a few hundred women a year, like those for rare diseases, enrollment becomes a slow crawl.

Also, these studies rely on volunteers. Only 15-20% of eligible women enroll. Those who do are often more informed, more anxious, or more motivated to contribute. That creates selection bias. The women who don’t join? We don’t know why. Maybe they’re scared. Maybe they don’t trust the system. Maybe their doctor never told them about the registry.

And even when data comes in, it takes years to analyze. A registry might start in 2020, collect data through 2024, and not publish findings until 2026. That’s too slow for a woman who’s pregnant right now.

Who Runs These Registries?

Most are funded by pharmaceutical companies-required by the FDA and EMA as part of post-market safety commitments. But they’re not run by the drugmakers. Independent research institutions manage them: hospitals, universities, nonprofit organizations like MotherToBaby.

In the U.S., over 80 active registries are currently tracking medications used in pregnancy. The biggest categories? Psychiatric drugs (12 registries), antiepileptics (8), and biologics for autoimmune diseases (15). These are areas where the benefit of treatment often outweighs the unknown risk. That’s why regulators push hardest here.

Europe and the U.S. have similar systems, but coordination is improving. In 2022, the FDA launched the Pregnancy Safety Research Network to standardize data collection across registries. That means better comparisons, fewer gaps, and eventually, more reliable conclusions.

What Women Say About Participating

Many women who join registries say it gives them peace of mind. One mother in Ohio, who took fluoxetine during her pregnancy and enrolled in the psychiatric registry, told researchers: “I didn’t want to be the one who didn’t tell anyone. I wanted to help the next woman.”

According to MotherToBaby’s 2022 report, 78% of participants felt they made a meaningful contribution. They appreciated getting personalized updates, even if the answers weren’t always clear. The biggest complaint? Not being able to get immediate answers. Registries aren’t urgent care-they’re long-term science.

But the emotional toll is real. Women taking psychiatric meds often feel guilty. They worry they’re harming their baby. Joining a registry doesn’t erase that fear, but it can turn it into something productive. For many, it’s the first time they’ve been asked: “What do you need to feel safe?”

The Future: Better Data, Smarter Systems

The next big step? Linking registries with electronic health records. Right now, data is collected manually-phone calls, paper forms, clinic visits. It’s slow. It’s error-prone. If registries could automatically pull data from EHRs-medication history, lab results, delivery notes-they’d get bigger, cleaner datasets without asking women to fill out more forms.

Researchers are also starting to use registry data alongside large insurance databases. A woman in a registry might be one of 500. But if you combine her data with 50,000 other pregnancies from claims systems, you get statistical power you never had before. This hybrid approach is already being tested.

And regulators are listening. The FDA’s 2023 Strategic Plan for Regulatory Science explicitly calls for integrating registry data with real-world evidence. That’s a game-changer. It means we won’t have to wait 10 years to learn if a drug is safe. We’ll start seeing patterns in 2-3 years.

What This Means for You

If you’re pregnant and taking medication, don’t stop without talking to your doctor. But do ask: “Is there a registry for this drug?” If there is, consider joining. You’re not just protecting your baby-you’re helping other women make better choices.

If you’re a healthcare provider, don’t assume your patient knows about registries. Mention them. Offer the contact info. Make it part of your routine counseling. Many women never hear about them unless someone brings it up.

And if you’re someone who’s ever wondered whether a medication is safe during pregnancy-you now know the answer isn’t simple. But it’s being built, one woman, one pregnancy, one registry at a time.