A UTI during pregnancy carries higher stakes than one outside of pregnancy. Left untreated, it can progress to a kidney infection and raise the risk of preterm birth. The good news: UTIs in pregnancy are common, well understood, and treatable with antibiotics that are safe for your baby. But the timing and type of treatment matter, and some UTIs don’t cause symptoms at all, which is why screening is a routine part of prenatal care.
Why Pregnancy Makes UTIs More Likely
Pregnancy changes your urinary tract in ways that make infections easier to develop. Rising progesterone levels relax the smooth muscle in your ureters (the tubes connecting your kidneys to your bladder), which slows the flow of urine. At the same time, your growing uterus presses on the bladder, making it harder to empty completely. Urine that sits in the bladder longer gives bacteria more time to multiply.
These changes start early and intensify as pregnancy progresses, which is why UTIs can happen in any trimester. The most common culprit is E. coli, the same bacterium responsible for most UTIs outside of pregnancy.
The Silent Version: Asymptomatic Bacteriuria
One of the trickiest aspects of UTIs in pregnancy is that bacteria can be present in your urine without causing any noticeable symptoms. This is called asymptomatic bacteriuria (ASB), and it affects roughly 2 to 10 percent of pregnancies. Outside of pregnancy, ASB is usually harmless and doesn’t need treatment. During pregnancy, it’s a different story.
Untreated ASB in pregnancy has a significant chance of progressing to a full-blown kidney infection (pyelonephritis). That’s why your provider will typically send a urine culture early in pregnancy, even if you feel perfectly fine. If bacteria show up above a certain threshold, you’ll be prescribed antibiotics regardless of whether you have symptoms. This single screening step prevents a large share of serious infections later in pregnancy.
What Can Happen If a UTI Goes Untreated
A simple bladder infection that isn’t treated can climb to the kidneys, causing pyelonephritis. Kidney infections during pregnancy are serious. They can lead to hospitalization, sepsis (a dangerous full-body response to infection), and respiratory complications for the mother. Pyelonephritis in pregnancy almost always requires IV antibiotics in a hospital setting.
The risks extend to the baby as well. Women with a UTI during pregnancy have roughly 2.5 times the risk of preterm birth compared to those without one, with about 12% of affected pregnancies delivering early in one large study. Preterm birth is the primary concern for the baby, as it can lead to low birth weight and time in the neonatal intensive care unit. These risks are why even a “minor” UTI in pregnancy is treated promptly and why asymptomatic infections are screened for proactively.
Symptoms to Watch For
A standard bladder UTI during pregnancy feels much like one at any other time: burning with urination, a frequent urgent need to go, cloudy or strong-smelling urine, and pelvic pressure. The challenge is that pregnancy itself causes frequent urination and pelvic discomfort, so it’s easy to dismiss early signs.
Certain symptoms suggest the infection has moved to your kidneys and warrant immediate medical attention:
- Fever above 100°F (37.8°C)
- Back or flank pain, especially on one side
- Chills
- Nausea or vomiting
- Mental changes or confusion
If you experience any combination of these, contact your provider right away or go to the emergency room. A kidney infection can escalate quickly during pregnancy.
How UTIs Are Treated During Pregnancy
For a straightforward bladder infection or asymptomatic bacteriuria, you’ll typically take an oral antibiotic for 5 to 7 days. The most commonly used options include cephalexin, nitrofurantoin, and fosfomycin (which is a single-dose option). Your provider will choose based on your urine culture results, the trimester you’re in, and any allergies you have.
Timing in pregnancy matters for antibiotic safety. Nitrofurantoin and sulfa-based antibiotics are generally avoided in the first trimester because of a possible link to birth defects when used that early. Sulfa-based antibiotics are also avoided late in the third trimester due to a small risk to the newborn after delivery. In those windows, cephalosporins like cephalexin are typically the go-to choice. Fluoroquinolones, a class of antibiotic commonly used for UTIs in non-pregnant adults, are not recommended during pregnancy.
If the infection has reached the kidneys, treatment is more intensive. Pyelonephritis in pregnancy usually means a hospital stay with IV antibiotics, often a cephalosporin. The oral antibiotics that work well for bladder infections, like nitrofurantoin and fosfomycin, don’t reach high enough concentrations in kidney tissue to be effective there.
What Happens After Treatment
After finishing your antibiotic course, your provider will likely order a follow-up urine culture to confirm the bacteria are gone. This matters because pregnancy’s ongoing physical changes mean reinfection is common. If the infection comes back, or if you’ve had multiple UTIs during the pregnancy, your provider may place you on a low daily dose of an antibiotic for the rest of the pregnancy to prevent recurrence. Common suppressive regimens include a daily dose of nitrofurantoin or cephalexin.
Recurrent UTI during pregnancy is typically defined the same way as outside of pregnancy: three or more infections within 12 months. The decision to start preventive antibiotics depends on your history, the bacteria involved, and how far along you are.
Reducing Your Risk
Standard UTI prevention advice applies during pregnancy: stay well hydrated, urinate frequently rather than holding it, wipe front to back, and empty your bladder after sex. These steps don’t guarantee prevention, but they reduce the opportunity for bacteria to establish themselves in a urinary tract that’s already working under extra strain.
Cranberry products have some supporting evidence in pregnancy. One randomized trial found that pregnant women who drank cranberry juice multiple times a day had a 57% reduction in asymptomatic bacteriuria and a 41% reduction in symptomatic UTIs compared to a placebo group. A separate study found that about 70% of pregnant participants who consumed cranberry juice reported fewer UTIs compared to 32% of those drinking water. Cranberry is considered safe during pregnancy, with a survey of 400 pregnant women detecting no adverse events from regular use, though some women find it causes gastrointestinal discomfort. Cranberry capsules tend to be better tolerated than juice, with one pilot study showing 82% compliance over six months.
D-mannose, a sugar supplement popular for UTI prevention outside of pregnancy, has very limited clinical evidence in pregnant women specifically, so its effectiveness and safety in pregnancy aren’t well established.