Pregnancy Registries: What We’re Learning About Medication Safety

When a woman finds out she’s pregnant, one of the first questions she asks is: Is this medication safe? Whether it’s an antidepressant, an epilepsy drug, or a biologic for rheumatoid arthritis, the answer is rarely simple. Most drugs haven’t been tested in pregnant women during clinical trials-ethically, they can’t be. So where do doctors and patients turn for real-world safety data? That’s where pregnancy registries come in.

What Are Pregnancy Registries, Really?

Pregnancy registries are not databases of side effects. They’re not emergency hotlines. They’re structured, long-term research studies that follow women who take medications during pregnancy-from the moment they start the drug through birth and sometimes beyond. These registries collect detailed, upfront information: exactly which drug, when it was taken, the dose, other meds being used, maternal health conditions, and lifestyle factors like smoking or alcohol. Then they track outcomes: Did the baby develop a birth defect? Was the baby born early? Was birth weight low? Did the child reach developmental milestones on time?

These registries exist because pre-approval trials exclude pregnant women. The thalidomide disaster in the 1960s, which caused thousands of severe birth defects, proved we can’t rely on animal studies alone. Today, the U.S. FDA and the European Medicines Agency (EMA) require companies to run these registries for certain drugs, especially biologics and those likely to be used by women of childbearing age. Since 2015, the FDA’s Pregnancy and Lactation Labeling Rule has made it even clearer: if a drug could be taken during pregnancy, safety data must be actively gathered.

How Do They Work in Practice?

Let’s say a woman with bipolar disorder finds out she’s pregnant and needs to stay on lithium. Her OB-GYN tells her about the National Pregnancy Registry for Psychiatric Medications. She calls, answers a few questions, and agrees to participate. Over the next year, she gets regular check-ins-sometimes by phone, sometimes online. She reports every doctor visit, every lab result, every ultrasound. After delivery, the registry team collects the baby’s medical records. Twelve months later, they ask: Is the child smiling, sitting up, babbling? That’s the kind of data you can’t get from a pharmacy claim or an electronic health record.

Unlike passive systems like the FDA’s Adverse Event Reporting System (FAERS), which waits for doctors or patients to report problems, registries go out and find participants. That’s why they’re called prospective studies. They capture exposure before outcomes happen, reducing the chance of recall bias. For example, a woman might forget she took a drug at week 6 if she’s asked six months later-but if she’s asked right away, the data is accurate.

What Have We Learned So Far?

The data from registries has changed how we think about medication use in pregnancy. For instance, earlier fears about SSRIs causing heart defects were largely debunked by registry data. Studies from the Massachusetts General Hospital registry showed no significant increase in major malformations with most antidepressants. That’s huge. It means thousands of women can now make informed choices instead of stopping life-saving meds out of fear.

For epilepsy drugs like lamotrigine, registries confirmed it’s among the safest options during pregnancy-unlike valproate, which carries a well-documented risk of neural tube defects. That’s led to clear clinical guidelines: avoid valproate if possible.

Even for newer drugs like biologics used for psoriasis or Crohn’s disease, registries have shown reassuring results. Drugs like adalimumab and infliximab don’t appear to increase the risk of major birth defects. That’s critical for women who need these drugs to stay healthy enough to carry a pregnancy.

But here’s the catch: registries don’t prove absolute safety. They can only tell us whether a drug is unlikely to cause a severe, obvious defect. They can’t catch tiny increases in rare risks. For example, if a drug raises the chance of a specific heart defect from 1 in 1,000 to 2 in 1,000, a registry might miss it unless it enrolls thousands of women. Most registries only have a few hundred participants.

The Limits: Small Numbers, Big Gaps

The biggest problem with pregnancy registries? Enrollment. Only about 15-20% of eligible women actually join. Why? Time. Fear. Confusion. Some women worry their data won’t be private. Others feel overwhelmed-“I just want to know if it’s safe now, not wait two years for a study.”

Registries also struggle with rare conditions. If a drug is only used by 50 pregnant women a year, it takes decades to gather enough data. That’s why drugs for rare autoimmune diseases or cancers still have vague labels: “Use only if benefit justifies risk.”

And there’s selection bias. Women who enroll are often more health-conscious, better educated, or have stronger support systems. That means the data might not reflect what happens to women with less access to care.

How Registries Compare to Other Methods

Some people suggest using insurance claims or electronic health records instead. But those systems have big holes. Did the woman actually take the drug? Was it prescribed for the right reason? Was the dose correct? Often, we don’t know. Plus, those records rarely track outcomes like developmental delays.

Case-control studies can be faster, but they rely on memory. A mother might not remember whether she took a drug at week 7 if her child has a defect six months later. Registries avoid that.

So registries aren’t perfect-but they’re the most reliable tool we have for catching serious risks early. The FDA calls them “essential” for drugs used by women of childbearing age. And they’re not going away.

What’s Changing Now?

In 2022, the FDA launched the Pregnancy Safety Research Network to link up 30+ registries under one standard. That means data can be pooled across studies. A drug studied in 200 women across three registries suddenly has 600 data points. That’s a game-changer.

New registries are expanding too. The National Pregnancy Registry for Psychiatric Medications added 18 new drugs in early 2024, bringing its total to 45. That includes newer antidepressants, antipsychotics, and mood stabilizers.

There’s also a push to integrate registry data with electronic health records. Imagine: a woman signs up, her doctor’s system automatically shares key data-meds, labs, ultrasound results-with her consent. That could cut enrollment time in half and reduce errors.

Experts like Dr. Sonia Hernandez-Diaz from Harvard say the future isn’t just registries-it’s a layered approach. Use registries to spot signals. Then use big databases to confirm them. That’s how we’ll get faster, clearer answers.

What This Means for You

If you’re pregnant or planning to be, and you’re on medication, don’t panic. Don’t stop cold. Talk to your provider. Ask: “Is there a registry for this drug?” If there is, consider joining. You’re not just helping yourself-you’re helping every woman who comes after you.

You’ll get personalized updates. You’ll learn what we know-and what we don’t. You might even get a report on your baby’s development. And you’ll be part of a system that’s slowly, steadily, making pregnancy safer for everyone.

Most women who join say they feel empowered. MotherToBaby, which runs several registries, found that 78% of participants felt they made a meaningful contribution. That’s not just data-it’s dignity.

Where to Find a Registry

You don’t have to hunt for them. Your OB-GYN, pharmacist, or psychiatrist can help. Many are run by academic medical centers like Massachusetts General Hospital or through nonprofit groups like MotherToBaby. The FDA website also lists active registries by drug class. If you’re taking a biologic, an antiepileptic, or a psychiatric medication, there’s likely a registry for it.

Don’t wait until you’re 20 weeks along. The earlier you enroll, the better the data-and the more you’ll know.