Pregnancy Registries: What We’re Learning About Medication Safety

When a woman becomes pregnant and needs to take medication, she often faces a terrifying question: Will this drug hurt my baby? For decades, doctors had little to go on. Clinical trials almost never included pregnant women-too risky, too complicated, too uncertain. So when a woman took antidepressants, blood pressure meds, or even insulin during pregnancy, she was essentially flying blind. That’s where pregnancy registries come in. These aren’t just databases. They’re lifelines. And what we’re learning from them is changing how we think about medication safety in pregnancy.

Why Pregnancy Registries Exist

The thalidomide tragedy of the 1960s shook the medical world. Thousands of babies were born with severe limb deformities because their mothers took a drug thought to be safe. That disaster forced regulators to ask: How do we know what’s safe during pregnancy? The answer wasn’t more lab tests. It was real-world data from real pregnancies. That’s how pregnancy registries were born.

Today, these registries are formal, structured studies that track women who take specific medications while pregnant. The U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) now require them for certain drugs-especially biologics, psychiatric medications, and antiepileptics. Why? Because pre-approval trials exclude pregnant women. So the only way to know if a drug causes birth defects is to watch what happens after it hits the market.

About 80% of pregnant women in the U.S. take at least one medication. That’s 4.8 million pregnancies a year where someone is using a drug with unclear safety data. Registries help fill that gap. They don’t just collect names and dates. They gather detailed information: exact drug, dosage, timing of exposure, other medications, smoking, alcohol, pre-existing conditions. Then they follow the baby-through birth, and sometimes up to a year after.

How Registries Work

Unlike passive systems that wait for doctors to report side effects, pregnancy registries go out and find participants. A woman might hear about one from her OB-GYN, her pharmacist, or a support group. She calls, answers a few questions, and if she qualifies, she’s enrolled. No pressure. No cost. Totally voluntary.

From there, the registry team checks in regularly. They ask: Did you have any complications? Was the baby born early? Any unusual features? Did the baby develop normally at 6 months? At 12 months? Some registries even track developmental milestones like sitting up, talking, or responding to names.

The National Pregnancy Registry for Psychiatric Medications, run by Massachusetts General Hospital, is one of the most detailed. It tracks over 45 medications-from SSRIs to mood stabilizers-and follows children up to age one. Why? Because some risks don’t show up at birth. They show up as delayed speech, learning difficulties, or behavioral issues later on.

Each registry is different. Some focus on one drug. Others cover a whole class-like all antiseizure medications. Enrollment numbers vary. Some have fewer than 50 women. Others have over 1,000. But even small numbers matter. If 3 out of 50 babies born to mothers taking a certain drug have a rare heart defect, that’s a signal. A red flag. Something worth investigating.

What We’ve Learned So Far

Registries have changed the story on several drugs. For example, before registries, many women stopped their antidepressants during pregnancy out of fear. But data from the National Registry showed that SSRIs like sertraline and citalopram didn’t increase the risk of major birth defects. That didn’t mean zero risk-but it meant the risk was low enough to weigh against the dangers of untreated depression.

Similarly, registries helped clarify risks around antiepileptic drugs. Valproate was once commonly prescribed. Then registry data showed a clear link to neural tube defects and lower IQ scores in children. That led to major changes in prescribing guidelines. Now, it’s rarely used in women who could become pregnant.

Even vaccines got clearer answers. The flu shot and Tdap (tetanus, diphtheria, pertussis) were once questioned. Now, registry data confirms they’re safe-and they protect both mother and baby. That’s huge. Because fear of vaccines during pregnancy still keeps some women from getting them.

But registries don’t give perfect answers. They can’t tell you if a drug increases the risk of a rare defect from 1 in 1,000 to 2 in 1,000. That’s too small to detect unless you have tens of thousands of participants. And that’s hard to get. Most registries rely on voluntary sign-ups. Only about 15-20% of eligible women enroll. Many are scared. Others don’t trust the system. Some just don’t have time.

The Limitations

No registry can prove a drug is 100% safe. That’s not how science works. What they can do is say: "We didn’t see a pattern of major birth defects." That’s reassuring-but not absolute.

A big problem? Selection bias. Women who join registries are often more health-conscious. They’re already talking to their doctors, asking questions, reading up. That means the data might not reflect women who don’t have access to care or who avoid medical advice.

Also, registries can’t compare apples to apples. If a woman takes a drug for severe depression, and her baby has a problem, is it the drug-or the illness itself? Depression can affect fetal growth. High blood pressure can cause preterm birth. Registries try to account for this, but it’s hard. That’s why experts now say registries should be paired with large database studies using electronic health records. The registry finds the signal. The database confirms the size.

Cost is another issue. Running a registry costs between $500,000 and $2 million a year. That’s why only drug companies are required to fund them-and only for certain high-risk drugs. There’s no registry for most over-the-counter meds, herbal supplements, or even common antibiotics.

What’s Changing Now

In 2022, the FDA launched the Pregnancy Safety Research Network to link up 80+ active registries across the U.S. They’re standardizing how data is collected, so findings from different studies can be combined. That’s a big deal. Instead of 10 tiny studies, you get one big one.

In 2024, the National Registry for Psychiatric Medications added 18 more drugs, bringing its total to 45. That’s the largest collection of its kind. And it’s not stopping. Researchers are now tracking not just birth defects, but long-term outcomes: ADHD, autism, anxiety, school performance.

Some registries are starting to pull data directly from electronic health records. Imagine: a woman takes a drug, her doctor enters it, and the registry automatically picks it up. No phone calls. No forms. Just quiet, accurate tracking. That could boost enrollment dramatically.

The goal isn’t to eliminate all uncertainty. It’s to reduce fear with facts. To give women real data, not myths.

What It Means for You

If you’re pregnant and taking medication, here’s the truth: you’re not alone. And you don’t have to guess.

Ask your doctor: "Is there a pregnancy registry for this drug?" If there is, consider joining. It’s not about helping the drug company. It’s about helping the next woman who comes after you. Your participation adds one more data point to a growing pile of evidence.

If you’re told to stop your medication because "it might be unsafe," ask for the data. What registry? What numbers? What study? Too often, fear drives decisions-not science.

And if you’re not on medication but know someone who is-share this. Many women never hear about registries. They think they have to choose between being healthy and having a healthy baby. Registries say: you don’t.

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