Pregnancy and ACE Inhibitors or ARBs: Fetal Risks and Safe Blood Pressure Alternatives
Stuart Moore 3 December 2025 9

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When you're pregnant and have high blood pressure, finding the right medication isn't just about managing your numbers-it’s about protecting your baby’s life. Many women don’t realize that common blood pressure drugs like ACE inhibitors and ARBs can cause serious, sometimes fatal, harm to a developing fetus. These medications, often prescribed for years before pregnancy, become dangerous the moment conception happens. The risks aren’t theoretical. They’re documented, repeated across global studies, and backed by every major medical organization in the world.

Why ACE Inhibitors and ARBs Are Dangerous in Pregnancy

ACE inhibitors (like lisinopril, enalapril, and ramipril) and ARBs (like losartan and candesartan) work by blocking the renin-angiotensin-aldosterone system, or RAAS. That’s fine for adults-it lowers blood pressure and protects the kidneys. But in a growing fetus, RAAS isn’t just helpful-it’s essential. It helps form the baby’s kidneys, regulates amniotic fluid, and supports healthy blood flow to the placenta.

When these drugs cross the placenta, they shut down that system. The result? Fetal kidneys stop working properly. Amniotic fluid drops dangerously low (a condition called oligohydramnios). The baby’s blood pressure plummets. Kidney failure can begin as early as the second trimester. Skull bones may not form correctly. In the worst cases, the baby dies in utero or is born with irreversible organ damage.

Studies show these risks aren’t limited to later pregnancy. A 2020 meta-analysis of 72 studies found that even exposure in the first trimester increases the chance of miscarriage, low birth weight, and premature birth. Earlier beliefs that first-trimester use was “safe” have been completely overturned. The American Heart Association and the American College of Obstetricians and Gynecologists (ACOG) now say there is no safe trimester for these drugs.

The Real Numbers Behind the Risks

It’s easy to hear “risk” and think it’s rare. But the data tells a different story. In one large study published in Obstetrics & Gynecology International, women taking ACE inhibitors or ARBs during pregnancy had a 25.4% miscarriage rate-more than double the 12.3% rate in women with similar health conditions who weren’t on these drugs. Babies exposed to these medications weighed, on average, 350 grams (nearly 13 ounces) less at birth. They were born nearly two weeks earlier than average.

The FDA classifies these drugs as Pregnancy Category D-meaning there’s clear evidence of human fetal risk. Their labels include a black box warning, the strongest possible alert. New Zealand’s Medsafe and the European Medicines Agency echo the same warning. Even the World Health Organization excludes them from its list of essential medicines for pregnant women.

And here’s the sobering part: despite all this, about 1.2% of pregnancies in women with chronic hypertension still involve accidental exposure to these drugs, according to FDA reports. That’s not because doctors are careless. It’s because many women are on these medications for years before they even know they’re pregnant. And not all providers consistently screen for pregnancy before prescribing them.

ARBs vs. ACE Inhibitors: Is One Worse?

You might wonder: if I’m on an ARB like losartan, is it safer than an ACE inhibitor like lisinopril? The answer is no-and ARBs may be even riskier.

Research from the American Heart Association shows that babies exposed to ARBs have worse outcomes than those exposed to ACE inhibitors. ARBs are linked to higher rates of neonatal death, more severe kidney damage, and longer hospital stays after birth. The reason? ARBs block a different part of the same system, but with longer-lasting effects. Once they bind to receptors, they stay there longer, making their impact more prolonged and harder to reverse.

Both classes are equally contraindicated. But if you’re planning pregnancy-or just found out you’re pregnant-switching away from an ARB is even more urgent than switching from an ACE inhibitor.

Split image: fragile sick fetus on left, healthy fetus protected by safe meds on right, surrounded by marigolds.

What Medications Are Safe During Pregnancy?

The good news? There are several well-studied, safe alternatives that work just as well-and without the fetal risks.

  • Labetalol: This is the first-line choice for most pregnant women. It’s a beta-blocker that also blocks alpha receptors, helping to lower blood pressure without reducing blood flow to the placenta. It’s been used safely since the 1980s. Dosing typically starts at 100 mg twice daily and can be increased up to 2,400 mg per day if needed.
  • Methyldopa: This is the oldest and most studied blood pressure medication for pregnancy. First used in the 1970s, it’s been given to millions of pregnant women with no link to birth defects. It’s especially helpful for women with chronic hypertension before pregnancy. The usual dose is 250 mg twice daily, increased gradually up to 3,000 mg per day.
  • Nifedipine: A calcium channel blocker, nifedipine is often used as a second-line option, especially when blood pressure spikes suddenly. It’s effective and safe for most women, though it’s used cautiously in those with heart failure because it can slightly weaken heart contractions.
These drugs don’t just lower numbers-they support healthy fetal growth. Studies show that when women switch from ACE inhibitors or ARBs to these alternatives early in pregnancy, birth weights and gestational ages return to normal ranges.

What Should You Do If You’re Already Pregnant?

If you’re currently taking an ACE inhibitor or ARB and just found out you’re pregnant, don’t panic-but don’t wait either.

Stop the medication immediately. Do not taper it yourself. Call your doctor or OB-GYN right away. They’ll need to switch you to a safe alternative within 24 to 48 hours. Delaying increases the risk of ongoing fetal damage.

Your provider will likely start you on labetalol or methyldopa and monitor your blood pressure closely. You may also need extra ultrasounds to check amniotic fluid levels and fetal growth. In some cases, fetal kidney function can be assessed through detailed anatomy scans.

It’s also important to know: if you were on these drugs before you knew you were pregnant, your baby is not automatically doomed. Many women who took them unknowingly in the first few weeks go on to have healthy babies. The key is stopping as soon as possible and switching to a safe alternative.

What If You’re Planning to Get Pregnant?

This is where prevention matters most.

If you’re a woman of childbearing age and take an ACE inhibitor or ARB for high blood pressure, talk to your doctor about switching before you try to conceive. Don’t wait for a missed period. Don’t assume “I’ll stop if I get pregnant.” Plan ahead.

The American College of Cardiology recommends that all women on these drugs receive counseling about pregnancy risks and be offered effective contraception if they’re not planning to conceive. But if you are planning pregnancy, your doctor should have already switched you to a safer medication-like labetalol or methyldopa-at least three months before you stop birth control.

This isn’t just about avoiding risks. It’s about giving your baby the best possible start. Healthy blood pressure before and during pregnancy reduces your risk of preeclampsia, preterm birth, and low birth weight-even without these drugs.

Doctor and patient at an altar of safe pregnancy medications, with discarded pills turning to dust.

What Your Doctor Should Be Doing

You shouldn’t have to be the one to remember this risk. Your provider should be proactive.

Every woman of childbearing age prescribed an ACE inhibitor or ARB should be asked:

  • Are you pregnant?
  • Are you planning to become pregnant?
  • Are you using reliable birth control?
If you’re not using birth control and you’re on one of these drugs, your doctor should either switch your medication or help you find a contraceptive method that works for you. This isn’t optional-it’s standard of care.

In 2023, ACOG and the Society of Obstetricians and Gynaecologists of Canada updated their guidelines to make this clear: “ACE inhibitors and ARBs must be discontinued immediately upon pregnancy confirmation.” That means every prescription should come with a warning, not just a pill bottle.

What to Do If You’ve Already Been Exposed

If you took an ACE inhibitor or ARB during early pregnancy and didn’t know you were pregnant, here’s what to do:

  1. Stop the medication immediately.
  2. Call your OB-GYN or maternal-fetal medicine specialist within 24 hours.
  3. Request a detailed anatomy ultrasound between 18 and 22 weeks to check for kidney abnormalities, low amniotic fluid, and growth issues.
  4. Ask about fetal echocardiography if your blood pressure has been high for a long time.
  5. Switch to a safe alternative like labetalol or methyldopa as soon as possible.
Many women in this situation feel guilt or shame. But remember: this isn’t your fault. These drugs are widely prescribed, and many women take them for years without knowing they’re dangerous in pregnancy. The goal now isn’t blame-it’s action.

Final Thoughts: Your Body, Your Baby, Your Power

High blood pressure during pregnancy is common. Managing it safely is possible. But ACE inhibitors and ARBs are not the answer. They’re outdated for this population, and the evidence against them is overwhelming.

If you’re on one of these drugs and thinking about pregnancy-or already pregnant-your next step is simple: talk to your doctor. Ask, “Is this medication safe during pregnancy?” If they hesitate or say, “It’s probably fine,” get a second opinion.

You have the right to safe, informed care. You also have the power to ask the right questions. Don’t let a routine prescription become a hidden danger. Your baby’s kidneys, lungs, and life depend on it.