How much does a urinary tract infection (UTI) increase the risk of preterm labor?

From the Guidelines

Urinary tract infections (UTIs) during pregnancy increase the risk of preterm labor by approximately 2-4 times, with a baseline risk of preterm birth in women with untreated asymptomatic bacteriuria (ASB) of about 53 per 1000, which may be reduced to approximately 14 per 1000 with antibiotic treatment. This increased risk occurs because the bacteria causing the UTI can trigger inflammation that releases prostaglandins and cytokines, which may stimulate uterine contractions and cervical changes. According to the most recent and highest quality study, antimicrobials may reduce the risk of preterm birth, with a risk difference of –39 [95% CI, –47 to –20] 1.

Key Points to Consider

• The risk of preterm labor is higher in women with UTIs, especially if the infection ascends to the kidneys (pyelonephritis) 1.
• Prompt treatment with pregnancy-safe antibiotics like nitrofurantoin, amoxicillin, or cephalexin is essential to reduce this risk 1.
• Pregnant women should also increase fluid intake, urinate frequently, and complete the full antibiotic course even if symptoms improve.
• Any pregnant woman experiencing UTI symptoms (burning urination, frequency, urgency) should contact their healthcare provider immediately for testing and treatment to minimize the risk of complications.

Management and Prevention

• Screening for and treatment of ASB in pregnancy is recommended to decrease the risk of pyelonephritis and preterm labor 1.
• Antibiotics probably lower the chance of very low birth weight from approximately 137 per 1000 to 88 per 1000 (RD, –49 [95% CI, –75 to –10]; moderate quality) 1.
• The generalizability of these observations is limited, and further evidence from other populations is necessary to evaluate the risks and benefits for all pregnant women and in settings with variable access to healthcare.

From the Research

UTI and Preterm Labor Risk

• Urinary tract infections (UTIs) are a common infection among pregnant women, affecting approximately 8% of pregnancies 2, 3.
• UTIs have been associated with an increased risk of preterm labor, with studies suggesting that women with symptomatic lower urinary tract infections are at increased risk for both preterm birth in general and spontaneous preterm birth at <37 weeks 4.
• The risk of preterm birth associated with UTIs is estimated to be around 2-3 times higher than in women without UTIs, with an adjusted odds ratio (OR) of 2.5 for preterm birth and 2.3 for spontaneous preterm birth at <37 weeks 4.
• UTIs have also been linked to other adverse pregnancy outcomes, including low birth weight, pyelonephritis, and sepsis 2, 5, 3.

Mechanisms and Associations

• The exact mechanisms by which UTIs increase the risk of preterm labor are not fully understood, but it is thought that intrauterine infection and the resulting inflammatory response may play a role 6.
• Toll-like receptors (TLRs) have been implicated in the recognition of pathogens and the initiation of the innate immune response, which may contribute to the onset of labor 6.
• The association between UTIs and preterm labor may be influenced by various factors, including the type and severity of the infection, the presence of other underlying medical conditions, and the effectiveness of treatment 5, 4.

Clinical Implications

• Screening for and treating asymptomatic bacteriuria has been shown to reduce the incidence of pyelonephritis in pregnancy, which may in turn reduce the risk of preterm labor 5, 3.
• Prompt diagnosis and treatment of UTIs is essential to minimize the risk of adverse pregnancy outcomes, including preterm labor 2, 5, 4, 3.