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

When you're pregnant and need to manage high blood pressure, the wrong medication can put your baby at serious risk. ACE inhibitors and ARBs - commonly prescribed for hypertension - are not safe during pregnancy. Even if you’re not trying to get pregnant, if you’re taking one of these drugs, you need to know the facts now.

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 a system in your body called the renin-angiotensin-aldosterone system, or RAAS. That system helps control blood pressure. But in a developing baby, it’s also essential for kidney growth and amniotic fluid production.

When a pregnant person takes these drugs, the baby’s kidneys can stop working properly. This leads to low amniotic fluid (oligohydramnios), which can cause lung underdevelopment, limb deformities, and skull abnormalities. The baby’s blood pressure can drop dangerously low. Their kidneys may fail. In severe cases, it leads to stillbirth or neonatal death.

Studies show these risks aren’t rare. A 2011 study published in Obstetrics & Gynecology International found that women taking ACE inhibitors or ARBs during pregnancy had a 25.4% miscarriage rate - more than double the rate in healthy controls. Babies exposed to these drugs were also born, on average, 1.8 weeks earlier and weighed about 350 grams less.

And here’s something many people still get wrong: it’s not just the second and third trimesters that are dangerous. A 2020 meta-analysis in Pharmacology Research & Perspectives showed that even exposure in the first trimester increases the risk of poor outcomes. There’s no safe window.

ARBs May Be Even Riskier Than ACE Inhibitors

While both classes are off-limits during pregnancy, evidence suggests ARBs carry a higher risk than ACE inhibitors. The American Heart Association’s 2012 review found that babies exposed to ARBs had worse outcomes - including more severe kidney damage and higher rates of neonatal complications - compared to those exposed to ACE inhibitors.

This matters because some patients assume if they took an ACE inhibitor early in pregnancy and stopped, they’re fine. But if they were on an ARB like losartan, the risk profile is more serious. The same goes for candesartan - it’s particularly linked to fetal toxicity. Both need to be stopped immediately.

What to Take Instead: Safe Alternatives for Hypertension in Pregnancy

You still need to control your blood pressure - but safely. Three medications are well-studied and recommended as first-line options during pregnancy:

• Labetalol: A beta-blocker that also blocks alpha receptors. It’s the most commonly used drug in pregnancy because it works quickly, has minimal side effects on the baby, and has decades of safety data. Doctors often start with 100 mg twice daily and increase as needed, up to 2,400 mg per day.
• Methyldopa: This has been used since the 1970s and has the longest track record of safety in pregnancy. It’s taken orally, usually starting at 250 mg twice daily, and can be increased up to 3,000 mg daily. It doesn’t cross the placenta much, so it rarely affects the baby’s heart rate or growth.
• Nifedipine: A calcium channel blocker that’s effective for high blood pressure. It’s often used as a second-line option, especially if labetalol or methyldopa aren’t enough. But it’s not ideal for women with heart failure or certain heart conditions because it can weaken heart muscle contractions.

These drugs don’t eliminate risk entirely - no medication is risk-free - but they’re proven to be far safer than ACE inhibitors or ARBs. Blood pressure targets during pregnancy are typically below 140/90 mmHg, unless there’s organ damage, which requires tighter control.

What Happens If You’re Already Pregnant and Taking One of These Drugs?

If you find out you’re pregnant and you’re on an ACE inhibitor or ARB, don’t panic - but act fast. Stop taking the drug immediately. Call your doctor the same day. Do not wait for your next appointment.

Your provider will switch you to one of the safe alternatives listed above, usually within 24 to 48 hours. They’ll likely order an ultrasound to check amniotic fluid levels and assess fetal kidney function. In many cases, if the drug is stopped early enough, the baby can recover without lasting damage - especially if exposure was limited to the first few weeks.

But if you’ve been taking it past the first trimester, your care team will monitor you closely for signs of fetal distress. That might mean more frequent ultrasounds, non-stress tests, and possibly early delivery if complications arise.

Planning a Pregnancy? Here’s What You Need to Do Now

If you’re taking an ACE inhibitor or ARB and thinking about getting pregnant, don’t wait until you miss a period. Talk to your doctor before you try to conceive.

Major medical groups - including the American College of Obstetricians and Gynecologists (ACOG), the American Heart Association (AHA), and the Society of Obstetricians and Gynaecologists of Canada (SOGC) - all agree: switch to a safer medication before pregnancy begins. That’s not a suggestion. It’s a standard of care.

Your doctor will help you transition slowly. You won’t just stop your current drug cold turkey - that could cause a dangerous spike in blood pressure. Instead, they’ll start you on labetalol or methyldopa, gradually reduce the ACE inhibitor or ARB, and make sure your blood pressure stays stable throughout the change.

Also, if you’re on birth control, make sure it’s reliable. Some forms of contraception - like the pill - can interact with blood pressure meds. Talk to your provider about the best combo for you.

Why Do These Mistakes Still Happen?

Despite clear guidelines, about 1.2% of pregnancies in women with chronic hypertension still involve exposure to ACE inhibitors or ARBs, according to FDA data from 2021. Why?

One reason: many patients don’t realize their blood pressure medication is risky. They see it as just a “pill for high blood pressure” and don’t connect it to pregnancy. Another reason: some providers don’t consistently ask about pregnancy plans or fail to document contraception use.

In New Zealand, Medsafe’s 2024 advisory now requires doctors to explicitly ask patients: “Are you planning to become pregnant?” and “Are you currently pregnant?” before prescribing these drugs. That’s the kind of practice that saves lives.

What You Should Do Right Now

If you’re a woman of childbearing age and take an ACE inhibitor or ARB:

• Check your pill bottle. Does it say “lisinopril,” “enalapril,” “losartan,” or “candesartan”? If yes, note the name.
• Ask yourself: Have I been told this is unsafe in pregnancy? If not, you need to ask.
• Schedule a call or appointment with your doctor. Don’t wait. Say: “I’m concerned about pregnancy and this medication. What are my safe options?”
• If you’re trying to get pregnant - or think you might be - stop taking the drug and switch to a safe alternative immediately.

This isn’t about fear. It’s about control. You can manage your blood pressure safely during pregnancy. You just need the right information and the right team.

Frequently Asked Questions