A UTI during pregnancy can be dangerous if left untreated, but it’s also very treatable when caught early. The real risk isn’t the infection itself so much as what happens when it goes unaddressed. An untreated bladder infection in a pregnant woman has a 25 to 35% chance of progressing to a kidney infection, a rate far higher than in non-pregnant women. That kidney infection can then trigger a cascade of serious complications including preterm labor, low birth weight, and in rare cases, maternal sepsis.
The good news: routine prenatal screening catches most infections early, and pregnancy-safe antibiotics resolve them quickly. Here’s what you need to know about the specific risks and what to watch for.
Why Pregnancy Makes UTIs More Risky
Pregnancy changes your urinary tract in ways that make infections both more likely and more dangerous. As the uterus grows, it compresses the ureters (the tubes connecting your kidneys to your bladder), which can slow urine flow and let bacteria multiply. Hormonal shifts also relax the smooth muscle in the urinary tract, making it easier for bacteria to travel upward from the bladder toward the kidneys.
This is why a simple bladder infection that might stay put in a non-pregnant person is much more likely to climb to the kidneys during pregnancy. About 40% of pregnant women with untreated bacteria in their urine go on to develop a symptomatic bladder infection, and 25 to 30% develop pyelonephritis, a kidney infection that typically hits in early pregnancy and often requires hospitalization.
What Can Happen if a UTI Goes Untreated
The complications of an untreated UTI during pregnancy fall into two categories: risks to you and risks to the baby.
For the mother, the most immediate danger is pyelonephritis. A kidney infection during pregnancy can lead to sepsis (a life-threatening bloodstream infection), severe anemia, and in rare cases, acute respiratory distress syndrome. These are serious, potentially life-threatening conditions that require emergency care.
For the baby, the concern centers on preterm birth and low birth weight. When bacteria release toxins into your system, your body responds with inflammation. That inflammatory response triggers the production of prostaglandins, the same chemical messengers your body uses to start labor contractions. Essentially, the infection can trick your body into contracting too early. Studies have documented preterm delivery in about 11% of pregnancies complicated by UTIs, and premature rupture of membranes (your water breaking too early) in about 6.3%.
There’s also emerging evidence of longer-term effects. A large study following over 243,000 deliveries found that children born to mothers who had a UTI during pregnancy were more likely to be hospitalized for infections during childhood, even after accounting for other risk factors like preterm birth. The increase was modest (about 24% higher risk) but statistically significant, suggesting that maternal infection may subtly influence a baby’s developing immune system.
The Silent Version: Bacteria With No Symptoms
One of the trickiest aspects of UTIs in pregnancy is that many are completely silent. Asymptomatic bacteriuria, meaning bacteria growing in your urine without causing any noticeable symptoms, affects roughly 2 to 10% of pregnant women. You feel perfectly fine, but the bacteria are there, and without treatment, they carry the same risk of progressing to a kidney infection.
This is why the American College of Obstetricians and Gynecologists recommends that every pregnant woman be screened with a urine culture early in prenatal care, regardless of symptoms. A standard urinalysis or dipstick test isn’t enough; only a culture can reliably detect low-level bacterial growth. If the initial screen is positive and treated, monthly follow-up cultures are generally recommended for the rest of the pregnancy to catch any recurrence.
Telling a UTI Apart From Normal Pregnancy Symptoms
Needing to pee constantly is one of the hallmark symptoms of both pregnancy and a UTI, which makes it easy to dismiss an infection as just another pregnancy inconvenience. The key differences are in how it feels, not how often it happens.
Normal pregnancy-related frequency feels like a full bladder and produces a normal stream when you go. A UTI adds pain or burning during urination, a persistent urgency even right after you’ve emptied your bladder, cloudy or strong-smelling urine, or pelvic pressure that feels different from the usual heaviness of pregnancy. Blood in the urine, even a faint pink tinge, is not a normal pregnancy symptom and warrants a call to your provider.
If the infection has reached your kidneys, the symptoms shift dramatically. Fever, chills, nausea, vomiting, and pain in your back or side (usually just on one side, near your lower ribs) signal pyelonephritis. These symptoms need urgent medical attention.
How UTIs Are Treated During Pregnancy
UTIs in pregnancy are always treated with antibiotics, even the asymptomatic kind. The goal is to clear the bacteria before they can travel to the kidneys or trigger complications. Treatment is short, typically lasting 3 to 7 days depending on the type and severity of the infection.
Not all antibiotics are safe at every stage of pregnancy. Some common UTI medications need to be avoided at specific times:
- First trimester: Trimethoprim (and combination drugs containing it) is avoided because it interferes with folate, a nutrient critical to early fetal development.
- Third trimester: Nitrofurantoin is typically avoided late in pregnancy because it can cause a type of blood cell breakdown in the newborn.
Antibiotics that are considered safe throughout the entire pregnancy include amoxicillin-clavulanate and several cephalosporin-class drugs. Your provider will choose based on which bacteria the culture identifies and what trimester you’re in. After treatment, a follow-up culture confirms the infection has cleared.
Reducing Your Risk
You can’t eliminate the anatomical and hormonal changes that make UTIs more common during pregnancy, but a few habits lower the odds. Stay well hydrated to keep urine flowing and flush bacteria out before they take hold. Urinate when you feel the urge rather than holding it. Wipe front to back. Empty your bladder after sex. Avoid douches and scented products near the urethra.
If you’ve had one UTI during pregnancy, your risk of getting another is higher, which is why ongoing screening matters. Keep all your prenatal appointments and mention any new urinary symptoms, even mild ones, between visits. Catching a UTI at the bladder stage is simple and low-risk. Catching it after it reaches the kidneys is a much bigger problem to solve.