A urinary tract infection (UTI) is an infection that can occur anywhere along the urinary tract. Women are already more prone to urinary tract infections (UTIs) than men, and their risk of developing them only increases during pregnancy. As many as 13 percent of pregnant women get UTIs, typically between their sixth and 24th week of pregnancy.
While an infection can develop in any part of the urinary system, most develop in the lower tract, often because bacteria has entered the system via the urethra and has begun to multiply in the bladder. The name of the UTI varies depending on the infection location:
- Urethritis: infection of the urethra (the tube that transports urine outside the body from the bladder)
- Cystitis: infection of the bladder
- Pyelonephritis: infection of the kidney
The most common of these is urethritis--descriptions below, unless otherwise specified, refer to this type of infection.
Causes of Urinary Tract Infections during Pregnancy
UTIs are primarily triggered by E. coli, a bacterium in the bowel that can inadvertently be transferred from to the urethra. While the body can usually remove or control microbes before an infection sets in, some of the biological and hormonal changes that occur during pregnancy increase a woman's susceptibility and decrease her ability to fight them off. These changes include:
- Ureteral dilation — Beginning at six weeks of pregnancy, the tubes that connect each kidney to the bladder (the ureters) widen. As the uterus grows it places increased pressure on the ureters, causing them to further dilate. Wider ureters allow bacteria to more easily enter the urinary system.
- Urinary stasis — When the uterus enlarges, it can obstruct the urinary tract and prevent urine from draining properly. If urine remains stationary for too long, the bacteria that are naturally found in urine have time to multiply and cause an infection.
- Increase in blood volume — Blood volume increases during pregnancy, something that increases blood flow to the kidneys, which end up making much more concentrated urine. Because highly-concentrated urine isn't as effective at removing bacteria from the urethra or bladder, any bacteria in the urinary tract can multiply over time.
- Glycosuria — Glycosuria is the presence of glucose or sugar in the urine, something that can happen during pregnancy as a result of inefficient kidney filtering. Bacteria feed on sugar, and any increase will prompt them to multiply.
- Decreased immune response — The decreased immunity that occurs during pregnancy to prevent rejection of the fetus also reduces the body's ability to fight infection.
Symptoms of Urinary Tract Infections during Pregnancy
Not all pregnant women with urinary tract infections will have symptoms. When symptoms do occur, they include:
- Painful urination
- Increased urge to urinate
- Cloudy or foul-smelling urine
- Blood in the urine (hematuria)
- Abdominal pain
- Pain during intercourse
Diagnosis of Urinary Tract Infections during Pregnancy
A urine analysis is often used to diagnose a UTI. The exam, which is done at all (or nearly all) prenatal visits, consists of a urine sample that is analyzed for the presence of bacteria. Pregnant women usually undergo this test at all (or nearly all) of their prenatal visits to ensure an infection has not developed. If the test is positive, the urine may be sent to a lab for further analysis to determine which bacteria are causing the infection and which drugs they are most susceptible to.
Treating Urinary Tract Infections during Pregnancy
Treatment of UTIs during pregnancy is necessary to prevent harm to the fetus. Left untreated, an infection can spread to the kidneys and cause early labor and low birth weight. The most common treatment for UTIs is a course of antibiotics, most of which are safe for pregnancy and highly effective.
Lee, M., Bozzo, P., Einarson, A., & Koren, G. (2008). Urinary tract infections in pregnancy. Canadian Family Physician, 54(6), 853-854.