When you’re pregnant and need to take a medication-whether it’s for depression, epilepsy, or an autoimmune condition-you’re not just thinking about yourself. You’re weighing every pill against the safety of your unborn child. But here’s the hard truth: pregnancy registries are the only real tool we have to answer that question with any kind of certainty. Clinical trials don’t include pregnant women. That’s ethical. But it leaves a massive gap in what we know. So who fills it? Pregnancy registries do. And what they’re learning is changing how doctors advise women every day.

Why Pregnancy Registries Exist

After the thalidomide disaster in the 1960s, where thousands of babies were born with severe limb deformities because their mothers took a then-approved sleeping pill, the medical world realized it couldn’t wait for tragedies to happen before acting. That’s when pregnancy registries began to take shape-not as a luxury, but as a necessity. Today, the U.S. Food and Drug Administration (FDA) and the European Medicines Agency (EMA) require these registries for certain drugs, especially biologics and psychiatric medications, as a condition of approval.

These aren’t passive databases. They’re active, structured studies. When a woman takes a medication during pregnancy, she can enroll. Registry staff collect detailed info: exact drug name, dosage, timing of exposure, other meds she’s on, her medical history, lifestyle habits like smoking or alcohol use. Then they follow her through delivery and beyond-tracking whether the baby was born early, had a low birth weight, or developed a major birth defect. Some even track development up to 12 months after birth.

This is critical because pre-market trials exclude pregnant women. Even if a drug looks safe in 5,000 non-pregnant adults, we still won’t know how it affects a developing fetus until it’s used by thousands of pregnant women. Registries are the only way to get that data without putting women at risk in a trial.

What We’ve Learned So Far

Over 80 active pregnancy registries are running in the U.S. alone, and they’ve already shifted medical practice. For example, data from the National Pregnancy Registry for Psychiatric Medications showed that certain SSRIs like sertraline carry a much lower risk of major birth defects than previously feared. That’s led to fewer women being taken off their meds during pregnancy-reducing the risk of untreated depression, which itself can harm fetal development.

Antiepileptic drugs like lamotrigine have also been re-evaluated. Earlier studies suggested high risk, but registry data showed that with proper dosing, the risk of cleft lip or palate was only slightly above baseline. That’s huge for women with epilepsy who need to stay on medication to avoid seizures.

Even biologics-expensive, complex drugs used for conditions like rheumatoid arthritis or Crohn’s disease-are being studied. Registry data from drugs like adalimumab and certolizumab now show no clear pattern of birth defects, allowing many women to continue treatment through pregnancy without fear.

But it’s not all good news. Some drugs still carry red flags. For instance, isotretinoin (Accutane) for acne remains a known teratogen, and registries help enforce strict pregnancy prevention programs. Others, like valproic acid, are now clearly linked to cognitive delays and neural tube defects-so much so that guidelines now say it should be avoided entirely in pregnancy if possible.

How Registries Compare to Other Methods

You might wonder: Why not just use hospital records or insurance claims? Those exist, and they’re used too. But they’re messy. Electronic health records often don’t capture exact drug doses or timing. Insurance claims might show a prescription was filled, but not whether the woman actually took it. And they can’t tell you if a woman had morning sickness, stopped taking the drug, or took it only in the first trimester.

Pregnancy registries avoid these problems by collecting data prospectively-before outcomes are known. That means less recall bias. If a woman remembers taking a pill on day 28 of her cycle, that’s far more accurate than trying to guess it six months later.

But registries have limits. They’re small. Most enroll between 50 and 1,000 women. To detect a rare defect that occurs in 1 in 100 births, you’d need over 1,200 exposed pregnancies to be 80% confident you’d notice a doubled risk. That’s rarely reached. That’s why experts say registries don’t prove safety-they help rule out major risks.

Think of it like this: If you’re trying to find a needle in a haystack, a registry is a small, careful hand-search of a few bales. Database studies are a metal detector sweeping the whole field. Neither is perfect. Together, they’re stronger.

Who Joins-and Why So Few Do

Enrollment is voluntary. And it’s hard. Only about 15-20% of eligible women who are offered participation actually sign up. Why? Time. Fear. Privacy concerns. Some worry their information could be shared with insurance companies or employers. Others feel overwhelmed already-doctor visits, ultrasounds, prenatal vitamins-and adding a registry feels like one more burden.

But those who do join often say it helps. MotherToBaby, which runs several registries, found that 78% of participants felt they made a meaningful contribution. Many appreciated getting personalized updates about the medication they were taking. One woman, taking lithium for bipolar disorder, told her registry counselor: “I didn’t want to be the one who didn’t know what was happening to my baby. I needed to know I wasn’t alone.”

Still, many women leave frustrated when they ask, “Is this safe?” and the registry staff can’t give a yes or no. That’s because registries are designed for long-term data collection, not instant answers. They’re not a hotline. They’re a research engine.

The Bigger Picture: Registries in a Changing System

The FDA launched the Pregnancy Safety Research Network in 2022 to link multiple registries together, standardize data, and increase statistical power. That’s a big step. Now, instead of 10 small studies, we’re starting to see pooled data from dozens. In 2024, the National Pregnancy Registry for Psychiatric Medications expanded to include 18 new drugs, bringing its total to 45. That’s the most comprehensive list of psychiatric meds studied in pregnancy anywhere in the world.

There’s also growing momentum to combine registry data with large health databases. Imagine a registry that automatically pulls in your lab results, ultrasound findings, and pediatric follow-ups from your electronic medical record. That’s the future-and it’s already being tested.

But challenges remain. Registries cost between $500,000 and $2 million a year to run. Many are funded by drug companies, which raises questions about bias-though all data is reviewed by independent scientists and published in peer-reviewed journals. And while 65% of new biologics approved between 2018 and 2022 required a registry, far fewer are required for older, generic drugs-even if they’re commonly used in pregnancy.

What This Means for You

If you’re pregnant and taking any medication-prescription, over-the-counter, or even supplements-talk to your provider about whether a registry is right for you. You might be eligible. You might not know it. And even if you’re not, the data from these registries is already helping your doctor make safer choices.

The bottom line: No drug is 100% proven safe in pregnancy. But registries are giving us the clearest picture we’ve ever had. They’re not perfect. They’re slow. They’re small. But they’re the only system we have that’s built specifically to protect the next generation.

What’s Next

The goal isn’t to replace registries. It’s to strengthen them. More integration with EHRs. Better outreach to underrepresented groups. Longer follow-up for neurodevelopmental outcomes. And most importantly-more women participating.

Because every woman who joins doesn’t just help herself. She helps the next woman who will face the same fear. And that’s how we turn uncertainty into evidence.