Causes of Leukocytes in the Urine During Pregnancy

Prenatal appointments frequently include urine testing, which can detect the presence of leukocytes (white blood cells) as well as red blood cells and substances such as glucose and protein. Causes of urine leukocytes during pregnancy are generally the same as for nonpregnant women. Urinary tract and genital infections are the most common culprits.

Causes of Leukocytes in the Urine During Pregnancy Credit: shironosov/iStock/GettyImages

Urinary Tract Infection

Urinary tract infections (UTIs) are common in women of childbearing age, with a slightly increased risk during pregnancy. While a UTI is usually a relatively minor problem for a nonpregnant woman, development of a UTI during pregnancy is more concerning because of potential complications for both the mother and her unborn baby. Leukocytes and bacteria in the urine are typical findings in a pregnant woman with a UTI, which can take different forms.

Lower UTI

A lower urinary tract infection refers to an infection limited to the bladder. Commonly known as a bladder infection or cystitis, symptoms associated with a lower UTI are typically limited to increased urinary urgency and frequency, and pain with urination.

Upper UTI

Pregnancy leads to changes in a woman's urinary tract that increase the likelihood that bacteria in the bladder will travel upward and infect one or both kidneys. This condition, known as an upper UTI or pyelonephritis, typically causes bladder infection symptoms along with additional symptoms, including:

  • Fever and chills
  • Flank pain (in the back below the rib cage)
  • Intermittent abdominal pain
  • Nausea, with or without vomiting
  • General feeling of being unwell

Asymptomatic Bacteriuria

Asymptomatic bacteriuria describes the presence bacteria in the urine, often with leukocytes, but without any of the symptoms associated with an upper or lower UTI. While this condition is often harmless in nonpregnant women, asymptomatic bacteriuria often progresses to pyelonephritis in pregnant women if left untreated.

Genital Infection

A genital infection during pregnancy -- including both sexually and nonsexually transmitted conditions -- can potentially lead to the presence of white blood cells in the urine. When one or more of these infections is present, vaginal and external genital secretions containing leukocytes often mix with the urine when collecting a sample. Examples of genital infections that might lead to finding white blood cells in the urine during pregnancy include:

  • Chlamydia
  • Vaginal yeast infection
  • Bacterial vaginitis
  • Gonorrhea
  • Genital herpes

Other Considerations, Warnings and Precautions

Pregnant women normally experience increased vaginal secretions that often contain leukocytes even when a woman does not have a genital infection. Cleansing the external genitalia with a hygienic wipe before collecting a urine sample avoids potential contamination with vaginal secretions -- and setting off false alarm bells.

Even if you have no leukocytes in your urine, the US Preventive Services Task Force and American Academy of Family Physicians recommend screening for asymptomatic bacteriuria with a urine culture between 12 to 16 weeks of pregnancy to reduce the risk of a kidney infection, premature labor and other possible complications. Treatment greatly reduces the risk of these complications. Talk with your pregnancy healthcare provider about the frequency of urine leukocyte testing, especially if you have diabetes, or a prepregnancy history of UTI or other urinary tract problems.

Contact your pregnancy healthcare provider without delay if you develop any symptoms of a bladder, kidney or genital infection. Early diagnosis and treatment minimize the risk of any potential complications for you and your unborn baby.

Reviewed and revised by: Tina M. St. John, M.D.

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