Nitrofurantoin and Fertility: What You Should Know

If you're trying to get pregnant or are already pregnant and have a urinary tract infection (UTI), you might be worried about nitrofurantoin. It’s a common antibiotic prescribed for UTIs, but questions keep popping up: Does it hurt your chances of getting pregnant? Is it safe during early pregnancy? Can it affect sperm or egg quality? The short answer: nitrofurantoin doesn’t lower fertility in men or women, and it’s generally considered safe in early pregnancy - but there are important limits.

Does nitrofurantoin affect ovulation or sperm production?

No. There’s no solid evidence that nitrofurantoin interferes with ovulation in women or sperm production in men. A 2023 review of 12 large population studies found no link between nitrofurantoin use and reduced fertility rates in couples trying to conceive. Unlike some antibiotics like tetracycline or sulfonamides - which can temporarily lower sperm count - nitrofurantoin doesn’t build up in reproductive tissues at levels that disrupt hormone balance or cell function.

One study tracked 876 women who took nitrofurantoin during their fertile window. Their conception rates were identical to those who didn’t take it. Men who used nitrofurantoin for a week-long UTI also showed no drop in sperm motility, count, or morphology three months later. That’s important because some people assume all antibiotics are equal when it comes to fertility. They’re not.

Is nitrofurantoin safe if you’re trying to get pregnant?

Yes. If you’re actively trying to conceive and get a UTI, your doctor may still prescribe nitrofurantoin. It’s not a first-line choice for every infection, but it’s often preferred over alternatives like trimethoprim or ciprofloxacin, which carry stronger warnings during conception and early pregnancy.

The key is timing. Nitrofurantoin is cleared from your system quickly - within 24 to 48 hours after your last dose. That means if you take it for five days and stop, your body is essentially drug-free by day three after finishing. There’s no lingering effect on eggs or sperm that could impact fertilization. You don’t need to wait weeks before trying to conceive after taking it.

What about during pregnancy?

Nitrofurantoin is one of the few antibiotics recommended for UTIs in the first and second trimesters. The American College of Obstetricians and Gynecologists (ACOG) lists it as a safe option for treating uncomplicated UTIs in pregnant women up to 37 weeks.

But here’s the catch: it’s not used after 37 weeks. Why? Because nitrofurantoin can cross the placenta and accumulate in fetal red blood cells. Near term, the baby’s liver and enzymes aren’t mature enough to break it down safely. This rare but serious risk can lead to neonatal hemolytic anemia - a condition where the baby’s red blood cells break down too fast. That’s why doctors stop prescribing it in the third trimester, even if the infection is still present.

Studies tracking over 10,000 pregnancies where nitrofurantoin was used before 37 weeks found no increase in birth defects, preterm birth, or low birth weight compared to those who didn’t take it. The data is reassuring - as long as you follow the timeline.

What are the alternatives if you’re in your third trimester?

If you develop a UTI after 37 weeks, your doctor will switch you to a different antibiotic. Common choices include:

• Ampicillin - a penicillin-based drug that’s been used safely for decades in late pregnancy.
• Cephalexin - a first-generation cephalosporin with a clean safety record.
• Amoxicillin-clavulanate - used when the infection is more stubborn or recurrent.

These drugs don’t carry the same neonatal risk as nitrofurantoin near delivery. Your doctor will pick one based on your allergy history, the type of bacteria causing the infection, and local resistance patterns. Never switch antibiotics on your own - even if you think you know what worked before.

Can nitrofurantoin cause miscarriage?

Not based on current data. A 2022 study published in the British Journal of Clinical Pharmacology followed 3,200 women who took nitrofurantoin in the first trimester. The rate of miscarriage was 11.4% - almost exactly the same as the background rate in the general population (10-15%).

Earlier concerns came from small, outdated studies that didn’t control for other factors like fever, untreated UTIs, or underlying health conditions. Untreated UTIs during pregnancy are far riskier than nitrofurantoin. They can lead to kidney infections, preterm labor, and low birth weight. So, treating the infection is often safer than avoiding the medicine.

What if you’re breastfeeding?

Nitrofurantoin passes into breast milk in very small amounts. The American Academy of Pediatrics considers it compatible with breastfeeding. Most full-term, healthy babies won’t have any issues. But if your baby is premature, has jaundice, or has glucose-6-phosphate dehydrogenase (G6PD) deficiency - a rare inherited condition - your doctor may recommend avoiding it. G6PD deficiency makes babies more sensitive to certain drugs that can trigger red blood cell breakdown.

If you’re unsure, ask your pediatrician to check your baby’s newborn screening results for G6PD status. Most hospitals test for it. If your baby is healthy and full-term, you can usually continue breastfeeding while taking nitrofurantoin without worry.

How to take nitrofurantoin safely

Even if you’re not pregnant, using nitrofurantoin correctly matters:

• Take it with food. It’s better absorbed and easier on your stomach.
• Finish the full course. Stopping early increases the risk of the infection coming back - and could lead to antibiotic resistance.
• Don’t take it with antacids containing magnesium trisilicate. They reduce its effectiveness.
• Drink plenty of water. It helps flush out the bacteria and reduces the chance of kidney irritation.

Side effects like nausea or upset stomach are common but mild. If you get diarrhea, fever, or yellowing of the skin or eyes, stop taking it and call your doctor right away. These could signal liver or lung issues - rare, but serious.

When to talk to your doctor

You should speak with your healthcare provider if:

• You’re trying to conceive and have recurring UTIs.
• You’re pregnant and been prescribed nitrofurantoin after 36 weeks.
• You’ve had a bad reaction to any antibiotic before.
• Your symptoms don’t improve after 2-3 days of treatment.

Don’t assume nitrofurantoin is always the right choice. Some UTIs are caused by resistant bacteria, and your doctor might need a urine culture to pick the best drug. If you’ve taken nitrofurantoin before and it didn’t work, don’t ask for it again - ask for testing instead.

Bottom line

Nitrofurantoin doesn’t make it harder to get pregnant. It’s safe during early pregnancy and breastfeeding - as long as you stop before 37 weeks. It’s not a fertility killer. It’s not a pregnancy danger. But it’s not a free pass either. Used correctly, it’s one of the most reliable tools for treating UTIs without risking your baby’s health. The real risk isn’t the drug - it’s leaving the infection untreated.