Pregnancy Registries: What We’re Learning About Medication Safety

When you’re pregnant and need to take a medication-whether it’s for depression, epilepsy, asthma, or an autoimmune condition-you’re not just thinking about yourself. You’re wondering: is this safe for my baby? The answer isn’t always clear. Most drugs aren’t tested on pregnant women during clinical trials. Ethical concerns, legal risks, and historical tragedies like thalidomide have left a gap in our knowledge. That’s where pregnancy registries come in. These aren’t just databases. They’re active, real-time efforts to track what happens when medicines are used during pregnancy-and what we’re learning is changing how we think about safety.

Why Pregnancy Registries Exist

Pregnancy registries were born out of necessity. After the thalidomide disaster in the 1960s, where thousands of babies were born with severe limb defects linked to a drug prescribed for morning sickness, the medical world realized it couldn’t wait for harm to happen before acting. Today, these registries are required by the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for certain drugs-especially biologics and medications likely to be used by women of childbearing age.

The goal? Find signals of harm early. Not to prove a drug is completely safe-that’s impossible-but to spot patterns that might mean trouble. A drug might look fine in a trial of 500 people. But if 10,000 pregnant women take it, and suddenly there’s a cluster of heart defects, that’s a red flag. Registries are designed to catch those signals.

Unlike passive systems like the FDA’s Adverse Event Reporting System (FAERS), which rely on doctors or patients to report side effects after the fact, pregnancy registries go out and find participants. They contact women as soon as they find out they’re pregnant and are taking a specific medication. Then they follow them-through birth, and often beyond.

How Registries Collect Data

It’s not just asking, “Did you take the drug?” It’s detailed. Registries track:

• Exactly which drug, dose, and when it was taken (first trimester? third?)
• Other medications or supplements the mother is using
• Her medical history-diabetes, high blood pressure, mental health conditions
• Lifestyle factors: smoking, alcohol, nutrition
• Pregnancy outcomes: miscarriage, preterm birth, birth weight
• Whether the baby has any major birth defects
• Developmental milestones up to 12 months after birth

Some registries, like the one run by Massachusetts General Hospital for psychiatric medications, even track how babies respond to touch, sound, and movement. That’s because some drugs might not cause visible birth defects-but could affect brain development later.

This data comes directly from the women themselves, their doctors, and sometimes hospital records. It’s collected prospectively-meaning before the outcome is known. That’s a big deal. Retrospective studies (looking back at medical records) often get it wrong because people forget what they took or misremember when.

What We’ve Learned So Far

The data from registries has changed the conversation around medication use in pregnancy. Here are a few real examples:

• Antidepressants (SSRIs): Early fears linked them to heart defects. But large registry data now show the risk, if any, is very small-less than 1%. The bigger risk? Untreated depression during pregnancy.
• Antiepileptic drugs: Valproate is known to carry a high risk of neural tube defects and cognitive delays. Registries confirmed this and led to strict warnings. Lamotrigine, on the other hand, shows a much cleaner profile.
• Biologics for autoimmune diseases: Drugs like Humira and Enbrel were once thought too risky. Registry data now show no increase in major birth defects, allowing many women to continue treatment safely.
• Vaccines: The COVID-19 mRNA vaccines were tracked in multiple registries. No increase in miscarriage, preterm birth, or birth defects was found-data that helped ease fears and boost vaccination rates.

These aren’t theoretical findings. They’re based on thousands of pregnancies. And they’re helping doctors make better choices. A woman with rheumatoid arthritis can now be told: “You can keep your medication. The registry data says your baby is likely fine.”

The Limits of Registries

But here’s the hard truth: registries can’t give you a guarantee. They’re powerful-but limited.

First, they’re small. Most registries enroll between 50 and 1,000 women. To detect a rare defect-say, one that happens in 1 out of 100 births-you’d need over 1,200 exposed pregnancies just to be 80% sure you’d notice if the risk doubled. That’s rarely reached.

Second, they’re voluntary. Only about 15-20% of women who are eligible actually sign up. That means the data might not represent everyone. Women who are more anxious, more informed, or more connected to their doctors are more likely to join. Those who are struggling with access, stigma, or fear might not.

Third, they can’t prove safety. They can only say: “We haven’t seen a clear signal of harm.” That’s not the same as “this is 100% safe.”

Dr. Allen Mitchell, a leading expert in birth defect research, puts it simply: “Registries can’t prove safety. But they can give you reassurance that a drug doesn’t carry a high risk for severe birth defects.”

Who Runs These Registries?

You might think drug companies run them-and they do. But it’s more complicated. Registries are often managed by academic medical centers in partnership with pharmaceutical sponsors. For example:

• The National Pregnancy Registry for Psychiatric Medications is run by Massachusetts General Hospital.
• MotherToBaby, a service of the Organization of Teratology Information Specialists (OTIS), operates registries for dozens of drugs and is funded by pharmaceutical companies but staffed by trained counselors.
• The Center for Birth Defects Research at the University of California works with the FDA on multiple registries.

These organizations don’t just collect data-they also provide free, confidential counseling to women who join. If you’re worried about your medication, you can call and get answers based on the latest registry findings. That’s huge for someone who’s scared and alone.

Challenges and Costs

Running a registry isn’t cheap. It costs between $500,000 and $2 million a year. That’s staff, phone lines, data entry, follow-up visits, and training. Many registries struggle to stay funded. Some shut down after a few years if enrollment is too low.

Retention is another problem. About 20-30% of women drop out before delivery. Life gets busy. Fear creeps in. Some women don’t want to be reminded they’re taking a medication during pregnancy.

And then there’s the emotional toll. A woman taking lithium for bipolar disorder might join a registry hoping for reassurance. But when she’s told, “We don’t know yet-it could take years to see results”-that’s not comforting. Registries aren’t designed to give instant answers. They’re designed for science.

The Future: Better Data, Bigger Picture

The field is evolving. In 2022, the FDA launched the Pregnancy Safety Research Network to link 15+ registries together, creating a shared database with standardized rules. That means more power to detect smaller risks.

Newer studies are combining registry data with electronic health records and insurance claims. This hybrid approach gives you the detailed exposure data from registries and the big sample size from databases. It’s like using a microscope and a telescope at the same time.

In 2024, the National Registry for Psychiatric Medications added 18 new drugs, bringing its total to 45. That’s progress. And the WHO now calls registries “the safety net we rely upon” to evaluate drugs in pregnancy.

But experts agree: registries are just one tool. They’re best used alongside other methods-like large population studies, animal research, and real-world data. No single system can give us the full picture.

What This Means for You

If you’re pregnant or planning to be, and you’re on medication:

• Don’t stop your meds without talking to your doctor. The risks of stopping might be higher than the risks of continuing.
• Ask if there’s a registry for your medication. You can search at MotherToBaby.org or ask your OB-GYN.
• Joining is voluntary, free, and confidential. You’re not just protecting your baby-you’re helping future moms.
• If you’re nervous, call a registry counselor. They don’t sell drugs. They give you facts based on real data.

You’re not alone. Over 80 active registries are running in the U.S. alone. And every woman who joins adds one more piece to the puzzle.

Final Thoughts

We used to say, “We don’t know if it’s safe.” Now, thanks to registries, we’re starting to say, “We know it’s likely safe-or we know what to watch for.” That’s progress. It’s not perfect. It’s slow. But it’s real.

The next time you hear someone say, “No one knows what happens when you take that drug during pregnancy,” you can say: “Actually, we’re learning. And it’s because women are stepping forward to help.”