UTIs are one of the most common infections during pregnancy. About one in six pregnant women will experience a urinary tract infection, with overall prevalence around 18% but ranging from 11% to 26% depending on geography and individual risk factors. That makes pregnancy a significant risk period for urinary infections, even in women who have never had one before.
Why Pregnancy Increases UTI Risk
Your urinary tract changes dramatically during pregnancy, starting earlier than most people realize. As early as seven weeks, the tubes connecting your kidneys to your bladder begin to widen. This happens because progesterone, one of the key hormones sustaining pregnancy, relaxes smooth muscle throughout the body, including the muscles lining your urinary tract. That relaxation slows the flow of urine, giving bacteria more time to multiply.
Later in pregnancy, the growing uterus physically compresses the ureters, especially on the right side, where the uterus naturally tilts. This creates a partial blockage that can cause urine to pool. By the third trimester, the bladder itself gets pushed upward and forward, shifting from a pelvic organ to more of an abdominal one. The bladder neck becomes distorted and funneled, making it harder to empty completely. Residual urine sitting in the bladder is an ideal environment for bacterial growth.
These hormonal and structural changes work together. Your body is essentially creating conditions where bacteria can enter the urinary tract, stay longer, and spread more easily than they would outside of pregnancy.
The Three Types of Pregnancy UTIs
Urinary infections during pregnancy fall into three categories, each with different implications.
Asymptomatic bacteriuria is the most common. Bacteria are present in the urine at significant levels, but you feel completely fine. No burning, no urgency, no pain. This is why it’s easy to miss without screening, and why it matters so much: without treatment, 20 to 35% of pregnant women with asymptomatic bacteriuria will go on to develop a symptomatic infection, potentially including a kidney infection.
Acute cystitis is what most people think of as a UTI. It involves the classic symptoms: frequent urination, burning or pain when urinating, urgency, and sometimes lower abdominal discomfort. During pregnancy, these symptoms can overlap with normal pregnancy changes like increased urination, which sometimes delays recognition.
Pyelonephritis is a kidney infection, and it’s the most serious form. Symptoms include fever, chills, back or flank pain, nausea, and vomiting. It can require hospitalization and poses real risks to both mother and baby. The progression from silent bacteria in the urine to a full kidney infection is the primary reason prenatal UTI screening exists.
How Screening Works
The American College of Obstetricians and Gynecologists recommends that every pregnant woman be screened for asymptomatic bacteriuria with a urine culture at an early prenatal visit. This is a standard part of prenatal care in the United States. A urine culture is more reliable than a simple dipstick test because it identifies the specific bacteria present and confirms whether the count is high enough to need treatment.
There isn’t a firm consensus on whether repeat screening is needed later in pregnancy if the initial culture comes back negative. Current guidelines note insufficient evidence to recommend for or against retesting, so practices vary. If you develop symptoms at any point, though, your provider will culture your urine regardless of earlier results.
Risks of Untreated Infections
Leaving a UTI untreated during pregnancy carries consequences beyond the discomfort of the infection itself. A meta-analysis of 11 studies found that urinary tract infections in pregnant women increased the risk of preterm delivery by 2.49 times compared to women without infections. A separate analysis of seven studies found the risk of low birth weight increased by 1.54 times.
These aren’t small numbers. Preterm birth is one of the leading causes of complications in newborns, and a preventable infection driving that risk is exactly the kind of thing early screening aims to catch. The progression from asymptomatic bacteriuria to pyelonephritis also puts mothers at risk for serious complications including sepsis, respiratory distress, and kidney damage. Treatment with antibiotics dramatically reduces these risks, which is why even symptom-free bacterial presence in the urine gets treated during pregnancy.
What Treatment Looks Like
Pregnancy-safe antibiotics are well established, and treatment for a straightforward UTI or asymptomatic bacteriuria is typically a short oral course. Your provider will choose an antibiotic based on the specific bacteria identified in your culture and its sensitivity profile. Some antibiotic classes commonly used outside pregnancy are avoided during certain trimesters due to potential effects on fetal development, so your provider’s selection will account for how far along you are.
After completing treatment, a follow-up urine culture is standard to confirm the bacteria have cleared. Recurrence is common enough during pregnancy that some women need more than one course of treatment. If infections keep returning, your provider may recommend a low-dose preventive antibiotic for the remainder of pregnancy.
Lowering Your Risk
While the hormonal and anatomical changes of pregnancy can’t be avoided, a few practical habits help reduce the chance of bacteria reaching your bladder. Staying well hydrated keeps urine flowing and reduces the time bacteria have to colonize. Urinating frequently, rather than holding it, helps flush bacteria before they can establish an infection. Emptying your bladder after sex reduces the bacterial load near the urethra. Wiping front to back after using the bathroom prevents intestinal bacteria from migrating toward the urinary tract.
None of these measures eliminate the risk entirely, which is why routine screening remains the most important safeguard. But they stack the odds in your favor, particularly if you’ve already had one UTI during the pregnancy and want to prevent another.