Pregnancy and ACE Inhibitors or ARBs: Fetal Risks and Safe Alternatives

When you’re pregnant and managing high blood pressure, the last thing you want is to accidentally harm your baby. Yet, some common blood pressure medications - ACE inhibitors and ARBs - are known to cause serious, sometimes fatal, damage to a developing fetus. These drugs aren’t just risky; they’re strictly forbidden during pregnancy. But if you’re on one of them and find out you’re pregnant, or you’re planning to conceive, what do you do next? The answer isn’t to panic - it’s to act fast, with clear guidance.

Why ACE Inhibitors and ARBs Are Dangerous in Pregnancy

ACE inhibitors (like lisinopril, enalapril, and captopril) 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. But in a growing baby, RAAS is critical for kidney development and amniotic fluid production. When this system gets shut down, the baby’s kidneys can’t function properly. That leads to low amniotic fluid (oligohydramnios), which can cause lung underdevelopment, limb deformities, and skull defects. The baby’s blood pressure can also crash, leading to poor circulation and organ failure.

Studies show these drugs don’t just cause rare birth defects - they’re linked to higher rates of miscarriage, premature birth, and stillbirth. One large study found that women taking ACE inhibitors or ARBs during pregnancy had a 25% chance of miscarriage, compared to just 12% in women with similar health conditions who weren’t on these drugs. Birth weights were, on average, 350 grams lower. Gestation was nearly two weeks shorter. And while early studies thought first-trimester exposure might be safe, newer data from 2020 proves that’s not true. Even exposure in the first 12 weeks increases the risk of serious problems.

ARBs May Be Even Worse Than ACE Inhibitors

You might think all RAAS blockers are equally dangerous. They’re not. While both classes are absolutely off-limits in pregnancy, research shows ARBs carry a higher risk than ACE inhibitors. The American Heart Association noted that babies exposed to ARBs had worse outcomes - more severe kidney damage, longer hospital stays, and higher chances of neonatal death. Losartan, one of the most commonly prescribed ARBs, has been tied to multiple cases of fetal death and irreversible kidney failure. Candesartan has shown similar patterns. Even though ACE inhibitors like lisinopril and enalapril are dangerous too, the damage from ARBs tends to be more severe and harder to reverse.

What Happens If You’re Already Taking One?

If you’re on an ACE inhibitor or ARB and just found out you’re pregnant, stop taking it immediately. Don’t wait for your next appointment. Don’t try to taper off. Just stop. Then call your doctor or OB-GYN right away. They’ll need to switch you to a safer medication as soon as possible - ideally within days. Delaying the switch increases the risk to your baby.

Doctors don’t just pull you off these drugs and leave you with uncontrolled blood pressure. They replace them with medications that have been used safely for decades in pregnant women. The two most trusted options are labetalol and methyldopa.

Safe Alternatives: Labetalol and Methyldopa

Labetalol is a beta-blocker that also blocks alpha receptors. It’s become the go-to first-line treatment for high blood pressure during pregnancy. It works quickly, crosses the placenta minimally, and has been studied in thousands of pregnancies with no clear link to birth defects or long-term harm. Most women start at 100 mg twice a day and can go up to 2,400 mg daily if needed. It’s well-tolerated, and side effects like dizziness or fatigue are usually mild.

Methyldopa has been used since the 1970s - longer than any other blood pressure drug in pregnancy. It’s a centrally acting agent that reduces nerve signals to blood vessels. It’s not flashy, but it’s proven. Over 100,000 pregnancies have been tracked, and it remains the gold standard for safety. Dosing starts at 250 mg twice daily and can be increased up to 3,000 mg per day. Some women report drowsiness or dry mouth, but these usually fade after a few weeks.

If those two don’t work well enough, nifedipine (a calcium channel blocker) is the next option. It’s effective and generally safe, but it’s not used as a first choice because it can lower blood pressure too fast or weaken heart muscle in women with pre-existing heart conditions. It’s reserved for cases where labetalol and methyldopa aren’t enough.

What About Other Blood Pressure Drugs?

Not all blood pressure medications are safe in pregnancy. Diuretics like hydrochlorothiazide can reduce blood volume too much, which hurts placental flow. Beta-blockers like atenolol have been linked to small-for-gestational-age babies and should be avoided. Angiotensin receptor-neprilysin inhibitors (ARNIs) like sacubitril/valsartan are even more dangerous than ARBs - they’re completely off-limits.

The key is to stick with the drugs that have decades of real-world use in pregnant women. That means labetalol, methyldopa, and sometimes nifedipine. Everything else carries unknown or unacceptable risks.

Prevention Is the Best Strategy

The most important step isn’t what you do after you get pregnant - it’s what you do before. If you’re a woman of childbearing age and you’re on an ACE inhibitor or ARB, talk to your doctor now. Don’t wait for a positive pregnancy test. Ask: “Is this drug safe if I get pregnant?” If it’s not, switch to a safer alternative before you try to conceive.

Major medical groups - the American College of Obstetricians and Gynecologists, the American Heart Association, the World Health Organization - all agree on this. You should be counseled about these risks before you even start the medication. If you’re planning a pregnancy, your blood pressure meds should be reviewed as part of your preconception care - just like folic acid and vaccines.

What If You’re Not Planning to Get Pregnant?

Even if you’re not trying to conceive, you still need to be careful. ACE inhibitors and ARBs can cause harm if you get pregnant without realizing it. That’s why doctors are required to ask: “Are you pregnant?” and “Are you planning to become pregnant?” before prescribing these drugs. If you’re sexually active and not using reliable birth control, your doctor should not give you an ACE inhibitor or ARB.

Effective contraception isn’t optional here. If you’re on one of these drugs, you need a backup plan - like an IUD, implant, or consistent use of oral contraceptives. Don’t rely on withdrawal or condoms alone. The stakes are too high.

Real-World Problems Still Happen

Despite all the warnings, mistakes still happen. FDA data from 2021 shows that 1.2% of pregnant women with chronic high blood pressure were still taking ACE inhibitors or ARBs. That’s not a lot - but it’s 1.2% too many. Some women don’t know their meds are risky. Others get prescribed them by a primary care doctor who doesn’t know they’re trying to conceive. Others stop taking them because they feel fine - only to have their blood pressure spike dangerously.

That’s why clear communication matters. If your OB-GYN doesn’t ask about your meds, ask them. If your pharmacist doesn’t warn you, ask them. If you’re switching doctors, bring your full medication list. Don’t assume someone else is checking.

Bottom Line: Stop, Switch, Stay Safe

ACE inhibitors and ARBs are not just “not recommended” during pregnancy - they’re dangerous. They can cause kidney failure, low amniotic fluid, miscarriage, and death. There is no safe trimester. No exception. No “it’s probably fine.”

If you’re pregnant and taking one: stop immediately. Call your doctor. Get switched to labetalol or methyldopa. You and your baby will be far safer.

If you’re planning to get pregnant: talk to your doctor now. Switch your meds before conception. Don’t risk it.

If you’re not planning to get pregnant: use reliable birth control. Don’t assume you’re safe just because you’re not trying.

High blood pressure during pregnancy is serious - but it’s manageable. With the right drugs, you can protect both your health and your baby’s. You don’t need to guess. You don’t need to hope. You just need to act.