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

When you're pregnant and have high blood pressure, the last thing you want is to take a medication that could harm your baby. Yet, many women with chronic hypertension are prescribed ACE inhibitors or ARBs before they even know they're pregnant. These drugs are common, effective, and widely used - but they are not safe during pregnancy. The risks aren't just theoretical. They're real, documented, and severe.

Why ACE Inhibitors and ARBs Are Dangerous in Pregnancy

ACE inhibitors and ARBs work by blocking the renin-angiotensin-aldosterone system (RAAS). That’s great for lowering blood pressure in adults. But in a developing fetus, that same system is essential for kidney growth, amniotic fluid production, and overall organ development. When these drugs cross the placenta, they shut down the baby’s RAAS. And that leads to serious, sometimes fatal, complications.

The risks include:

• Fetal kidney failure - the baby’s kidneys stop working properly
• Oligohydramnios - dangerously low levels of amniotic fluid, which can cause lung underdevelopment and limb deformities
• Fetal skull defects - including flattened facial bones and underdeveloped skull bones
• Severe low blood pressure in the newborn
• High potassium levels (hyperkalemia) - which can cause heart rhythm problems
• Stillbirth or neonatal death

A 2011 study in Obstetrics & Gynecology International found that women taking ACE inhibitors or ARBs during pregnancy had a 25.4% miscarriage rate - nearly double the rate of women with similar health conditions who weren’t on these drugs. Even more alarming, babies exposed to these medications were born, on average, 1.8 weeks earlier and weighed 350 grams less than babies not exposed.

And here’s the hard truth: it’s not just second or third trimester exposure that’s dangerous. A 2020 meta-analysis published in Pharmacology Research & Perspectives showed that even taking these drugs in the first trimester increases the risk of adverse outcomes. Earlier beliefs that first-trimester use was “safe” have been thoroughly debunked.

ARBs May Be Even Riskier Than ACE Inhibitors

Not all drugs in this category carry the same level of risk. While both ACE inhibitors and ARBs are strictly off-limits during pregnancy, research shows ARBs like losartan and candesartan are associated with worse outcomes than ACE inhibitors like lisinopril or enalapril.

The American Heart Association’s 2012 review found that babies exposed to ARBs had poorer neonatal outcomes - including higher rates of kidney failure and death - compared to those exposed to ACE inhibitors. This isn’t a small difference. It’s a clinically significant one. And it’s why guidelines now treat both classes the same: no safe window, no safe dose.

Common ACE inhibitors linked to fetal harm include:

• Enalapril
• Lisinopril
• Perindopril
• Quinapril
• Ramipril

Common ARBs include:

• Losartan
• Candesartan
• Valsartan
• Irbesartan

These drugs are labeled with FDA boxed warnings - the strongest kind - for fetal toxicity. The European Medicines Agency and the World Health Organization agree: these medications should never be used during pregnancy.

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

If you find out you’re pregnant while taking an ACE inhibitor or ARB, don’t panic - but do act fast. Stop the medication immediately. Then contact your doctor right away.

The goal isn’t to leave you with uncontrolled blood pressure - that’s dangerous too. It’s to switch you to a safer option as quickly as possible. Delaying the switch increases the risk to your baby. Studies show that the longer you’re exposed to these drugs during pregnancy, the worse the outcomes.

Your doctor will likely switch you to one of three well-studied, pregnancy-safe alternatives:

Safer Alternatives for Managing High Blood Pressure During Pregnancy

There are three main antihypertensive medications with decades of safety data in pregnancy. These are the gold standard:

1. Labetalol - First-Line Choice

Labetalol is a beta-blocker that also blocks alpha receptors. That means it lowers blood pressure without significantly reducing blood flow to the placenta. It’s been used safely since the 1980s and is now the go-to first-line drug in most guidelines, including those from the American College of Obstetricians and Gynecologists (ACOG) and Health New Zealand.

Starting dose: 100 mg twice daily. Can be increased up to 2,400 mg per day, divided into two or three doses. Most women tolerate it well. Side effects are mild - maybe some fatigue or dizziness, but rarely anything serious for the baby.

2. Methyldopa - The Longest Track Record

Methyldopa has been used in pregnancy since the 1970s. More than 50 years of data show it’s safe for both mother and baby. It works by calming the central nervous system to reduce blood pressure. It doesn’t cross the placenta in large amounts, and there’s no evidence of harm to fetal development.

Starting dose: 250 mg twice daily. Can be increased to 3,000 mg per day in divided doses. Some women report drowsiness or dry mouth, but these usually fade over time.

3. Nifedipine - Second-Line Option

Nifedipine is a calcium channel blocker. It’s often used when labetalol or methyldopa aren’t enough, or if a woman can’t tolerate them. It’s effective and generally safe - but it’s not ideal for women with heart conditions because it can slightly reduce the heart’s pumping strength.

Immediate-release forms are preferred in pregnancy. Extended-release versions aren’t recommended because their absorption is unpredictable.

What About Other Blood Pressure Medications?

Some women ask: “What about diuretics? Or angiotensin receptor-neprilysin inhibitors (ARNIs)?”

Diuretics like hydrochlorothiazide were once commonly used, but they’re now avoided in pregnancy because they can reduce blood volume and placental flow, potentially leading to low birth weight. ARNIs like sacubitril/valsartan are newer drugs - and they’re absolutely contraindicated. They contain an ARB component, so they carry the same risks.

Even over-the-counter NSAIDs like ibuprofen or naproxen can be risky in the third trimester. Always check with your doctor before taking anything.

Planning Pregnancy? Get Ahead of the Risk

The best time to switch medications is before you get pregnant. If you’re on an ACE inhibitor or ARB and thinking about starting a family, talk to your doctor now. Don’t wait for a positive pregnancy test.

Your healthcare provider should:

• Ask if you’re planning to become pregnant
• Discuss your options and risks
• Switch you to a safer drug before conception
• Confirm you’re using reliable contraception if you’re not ready to get pregnant

The American College of Cardiology and Medsafe both emphasize this: women of childbearing age on ACE inhibitors or ARBs must receive counseling about these risks. It’s not optional. It’s standard care.

What If Your Doctor Doesn’t Mention This?

Sadly, medication errors still happen. According to the FDA’s 2021 adverse event data, about 1.2% of pregnancies in women with chronic hypertension still involve exposure to ACE inhibitors or ARBs. That’s not because doctors are careless - it’s because these drugs are so common, and pregnancy isn’t always planned.

If you’re taking one of these drugs and haven’t been warned about pregnancy risks, speak up. Ask: “Is this safe if I get pregnant?” If your provider doesn’t know, ask for a referral to a maternal-fetal medicine specialist or a pharmacist who specializes in pregnancy.

You have the right to know. And you deserve to be protected.

What to Do Next

If you’re currently taking an ACE inhibitor or ARB:

• If you’re pregnant: stop the drug immediately and contact your provider today.
• If you’re trying to conceive: schedule an appointment to switch medications before you stop contraception.
• If you’re not planning pregnancy: ask your doctor about reliable birth control options that work with your current meds.

There’s no reason to risk your baby’s health. Safe, effective alternatives exist. You don’t have to choose between controlling your blood pressure and protecting your pregnancy.