Is It Safe to Take Nitrofurantoin While Pregnant?

Nitrofurantoin is widely considered safe during pregnancy, particularly in the second and third trimesters, where it is a first-line antibiotic for bladder infections. The first trimester is where the picture gets murkier: some studies have flagged a small possible increase in certain birth defects, while others find no meaningful risk. Major obstetric guidelines still allow nitrofurantoin in early pregnancy when better alternatives are not available, reflecting a consensus that the real-world risk, if it exists at all, is small and that leaving a urinary tract infection untreated carries its own dangers.

Why UTIs in Pregnancy Get Taken Seriously

Urinary tract infections are common during pregnancy. Hormonal changes relax the muscles of the urinary tract and the growing uterus presses on the bladder, both of which make it easier for bacteria to stick around and multiply. What makes this a genuine clinical concern, rather than a minor nuisance, is that untreated UTIs in pregnant people are more likely to progress to kidney infections. Acute pyelonephritis during pregnancy has been linked to increased maternal complications, and some research connects it to preterm delivery and low birth weight.

Even infections that cause no symptoms can be a problem. Asymptomatic bacteriuria, where bacteria show up in a urine culture but the person feels fine, occurs in a meaningful percentage of pregnancies. Current guidelines recommend screening with a urine culture early in prenatal care, because treating asymptomatic bacteriuria appears to reduce the chances of low birth weight and preterm birth. A simple dipstick test at each visit is not sensitive enough to catch it; a proper culture is needed.

The First Trimester Question

The first trimester is when a baby’s organs are forming, so any medication used during those early weeks gets extra scrutiny. For nitrofurantoin, the safety picture in the first trimester is genuinely mixed, and that ambiguity is worth understanding rather than glossing over.

One of the more widely cited concerns came from a large U.S. study that found statistical associations between first-trimester nitrofurantoin use and a few specific birth defects, including certain heart defects and cleft lip with cleft palate. The adjusted odds ratios ranged from roughly 2 to 4 for these individual defects, which sounds alarming in isolation.

But context matters. A systematic review and meta-analysis pooling data from multiple studies found that cohort studies, which follow large groups of women forward in time, showed no increased risk of major malformations overall. Case-control studies, which work backward from babies born with defects, did find a slight increase, with an odds ratio of about 1.22. The researchers noted that case-control designs are more sensitive to detecting small risks but are also more vulnerable to certain biases, particularly recall bias when mothers are asked to remember medications from early pregnancy.

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A large 2025 study added another layer. When researchers compared babies exposed to nitrofurantoin in the first trimester against babies whose mothers took beta-lactam antibiotics instead, the risk of any malformation was similar between the two groups. The weighted relative risk was 1.12, with the confidence interval just touching 1.0 on the lower end, meaning the result hovered right at the boundary of statistical significance. In practical terms, the estimated difference was roughly two to three extra cases of any malformation per 1,000 births, and even that small bump might be explained by factors other than the drug itself.

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The American College of Obstetricians and Gynecologists (ACOG) summarizes the situation by noting that data on first-trimester congenital anomalies are “mixed and have methodologic limitations.” Their recommendation: nitrofurantoin is reasonable in the first trimester if no appropriate alternatives are available. It is not banned or contraindicated; it just sits a step behind options like certain penicillins or cephalosporins when those work.

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Second and Third Trimesters

Once the first trimester passes, the safety profile of nitrofurantoin improves considerably. Organ formation is largely complete, and the drug’s theoretical risk to fetal development drops. ACOG explicitly endorses nitrofurantoin as a first-line treatment for lower urinary tract infections in the second and third trimesters. It concentrates well in the bladder, where it needs to work, and maintains low resistance rates against the bacteria most commonly responsible for UTIs in pregnancy.

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An older retrospective analysis of 91 pregnancies in which nitrofurantoin was used found no increase in fetal death, neonatal death, malformation, prematurity, low birth weight, or jaundice compared to background rates. None of the adverse events in the study were considered drug-related.

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The one timing caveat involves use very close to delivery. A case report documented hemolytic anemia in a newborn whose mother had taken nitrofurantoin during the last month of pregnancy. Newborns have immature enzyme systems that make them more vulnerable to the oxidative stress nitrofurantoin can cause in red blood cells. Because of this, most clinicians prefer to avoid the drug in the final two to four weeks before the expected delivery date, or once labor appears imminent.

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G6PD Deficiency and Who Should Avoid Nitrofurantoin

Glucose-6-phosphate dehydrogenase (G6PD) deficiency is an inherited enzyme condition that makes red blood cells unusually fragile when exposed to certain drugs. Nitrofurantoin is one of those drugs. In people with G6PD deficiency, it can trigger hemolytic anemia, where red blood cells break down faster than the body can replace them. Research has shown that nitrofurantoin dramatically shortens red blood cell survival in G6PD-deficient individuals.

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G6PD deficiency is more common in people of African, Mediterranean, Middle Eastern, and Southeast Asian descent. ACOG specifically warns against using nitrofurantoin in patients with this condition, noting associations with pulmonary toxicity and hemolytic anemia.

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If you know you have G6PD deficiency, or if it runs in your family and you have not been tested, this is something to bring up with your provider before taking nitrofurantoin. The concern applies outside of pregnancy too, but the stakes feel higher when two people’s health is involved. Alternative antibiotics should be chosen instead.

How a Protective Placental Protein Works in Your Favor

One reason nitrofurantoin appears relatively safe during mid-pregnancy is that the placenta actively limits how much of the drug reaches the fetus. A protein called breast cancer resistance protein (BCRP), present on the placental barrier, pumps nitrofurantoin back toward the maternal side. Mouse studies showed that when this protein was absent, fetal exposure to nitrofurantoin was roughly five times higher than in normal mice, while the mother’s blood levels barely changed. In other words, the placenta is doing meaningful work to keep the drug away from the baby.

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This finding is from animal research, so it cannot be directly mapped onto human pregnancies. But BCRP is present in the human placenta too, and the principle is reassuring: the body has a built-in mechanism to reduce fetal drug exposure. Whether this protection is fully operational in the earliest weeks of pregnancy, before the placenta is mature, is less clear, which may be part of why the first trimester remains the period of greatest uncertainty.

How Nitrofurantoin Stacks Up Against Other Options

A pregnant person with a bladder infection does not have unlimited antibiotic choices. Some classes are outright avoided in pregnancy, and among the safer options, local resistance patterns can limit what actually works.

ACOG recommends against starting empiric treatment with amoxicillin or ampicillin alone because resistance rates for E. coli, the most common UTI-causing bacterium, tend to be high in most regions. Nitrofurantoin, by contrast, maintains low resistance rates against many of the pathogens common in pregnancy and concentrates effectively in the bladder.

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One alternative worth knowing about is fosfomycin, a single-dose antibiotic. A randomized trial comparing a single three-gram dose of fosfomycin against a seven-day course of nitrofurantoin found cure rates of 95% and 92%, respectively, with better compliance in the fosfomycin group, which makes sense given that taking one dose is simpler than remembering a pill for a full week.

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Resistance is not uniform across all bacteria, though. One cross-sectional study found that while E. coli was broadly susceptible to nitrofurantoin, other organisms like Pseudomonas aeruginosa and Staphylococcus saprophyticus showed high resistance to it. This underscores why a urine culture with sensitivity testing is so important: what works for one infection might not work for another, and the answer depends on which bug is causing the problem.

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Using Nitrofurantoin to Prevent Recurrent Infections

Some pregnant people do not just get one UTI; they get them repeatedly. For those with a history of recurrent infections, low-dose prophylactic nitrofurantoin can be effective. One study tracked 33 women with histories of recurrent UTIs, some of whom had previously developed kidney infections. They were given a single low dose of either nitrofurantoin (50 mg) or cephalexin after intercourse. Before starting prophylaxis, these women had accumulated 130 UTIs over an average observation period of seven months. After starting prophylaxis, only a single UTI occurred across all the pregnancies.

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For women who have already had a kidney infection during pregnancy, long-term low-dose prophylaxis is another option. In one study, 23 women took 50 mg of nitrofurantoin nightly after completing treatment for acute pyelonephritis and continued until a month after delivery. There were zero breakthrough infections during a combined 7.8 patient-years of treatment, and the regimen was well tolerated.

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How Long You Take It Matters

If you are prescribed nitrofurantoin for asymptomatic bacteriuria, the standard course is seven days. A randomized trial compared a single-day course against a seven-day course and found that the longer regimen produced significantly better cure rates: about 86% versus 76%. The seven-day group also had slightly higher birth weights and longer gestational ages on average, with roughly 100 grams and a fraction of a week separating the two groups. Adverse effects were similar between the regimens, so the longer course does not seem to come at a cost in terms of side effects.

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Finishing the full course matters here. The temptation to stop early once symptoms improve (or if you never had symptoms to begin with) can lead to incomplete bacterial clearance and a relapse of infection, which just means more antibiotics later.

Rare Maternal Side Effects

Most pregnant people tolerate nitrofurantoin without trouble, but rare maternal side effects do exist and are worth knowing about. The most serious is pulmonary toxicity: an acute lung reaction that can cause breathing difficulty, chest pain, and cough. Although this is a known side effect of nitrofurantoin in the general population, it was long thought not to occur in pregnancy. A case report documented respiratory failure in a woman at 16 weeks of gestation who was taking the drug for a UTI, demonstrating that pregnant patients are not immune.

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Liver damage is another rare possibility. A case of acute toxic hepatitis was documented in a 31-year-old woman in her 36th week of pregnancy who was taking 100 mg of nitrofurantoin daily. Her liver enzyme levels climbed, but they returned to near normal after the drug was stopped and brief treatment with corticosteroids was given.

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These are genuinely rare events, and they are not unique to pregnancy. But if you develop unexplained shortness of breath, chest pain, or yellowing of the skin while on nitrofurantoin, contact your provider promptly. Catching these reactions early and stopping the drug typically leads to full recovery.

Childhood Leukemia and Other Long-Term Concerns

One question that has received attention in recent years is whether prenatal antibiotic exposure could influence a child’s risk of cancer later on. A large registry-based study across four Nordic countries examined whether children exposed to nitrofurantoin in utero had higher rates of childhood leukemia compared to children whose mothers took a different common antibiotic (pivmecillinam). The incidence rate ratio was 1.34, but the confidence interval was wide and crossed 1.0, meaning the result was not statistically significant. The estimated difference worked out to about 15 extra cases per million person-years, and there was no evidence that higher doses correlated with higher risk.

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This is the kind of finding that is difficult to interpret cleanly. The study was well-designed and large, but the lack of statistical significance means we cannot confidently say there is a real effect. It does not mean there is definitely no effect either. For now, this falls into the category of a signal worth monitoring but not one that changes clinical practice. No major guideline has altered its recommendations based on this data, and the absolute numbers involved, even if the association were real, are very small.

What Nitrofurantoin Cannot Treat

One important limitation: nitrofurantoin only works for lower urinary tract infections. It concentrates in the urine but does not reach high enough levels in the bloodstream or kidney tissue to treat a kidney infection (pyelonephritis). If a bladder infection progresses, or if you develop fever, back pain, nausea, or vomiting alongside urinary symptoms, that suggests the infection has moved beyond the bladder, and a different antibiotic, typically a beta-lactam given intravenously, is needed. This is not a failing of nitrofurantoin so much as a consequence of how it works. Its specificity for the bladder is what makes it effective and well-tolerated there, but that same property limits where it can be used.

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