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What Are the Causes of Leukocytes in the Urine in Pregnancy?

author image Amber Canaan
Amber Canaan has a medical background as a registered nurse in labor and delivery and pediatric oncology. She began her writing career in 2005, focusing on pregnancy and health. Canaan has a degree in science from the Cabarrus College of Health Sciences and owns her own wellness consulting business.
What Are the Causes of Leukocytes in the Urine in Pregnancy?
A pregnant woman is going over a urine test result with her doctor. Photo Credit pojoslaw/iStock/Getty Images


During pregnancy, routine urine testing is often performed at each prenatal appointment. These tests can detect the presence of leukocytes, or white blood cells. Leukocytes are usually caused by inflammation. There are several reasons why leukocytes may appear in the urine of a pregnant woman.

Urinary Tract Infection

Frequently, an infection of the urinary tract is to blame for the presence of leukocytes in the urine. These infections are one of the most common medical issues during pregnancy. Women have an increased bladder volume but decreased bladder tone due to the weight of the baby. Complete emptying of the bladder can be difficult, allowing for bacteria to grow and multiply. An infection of the bladder may then develop, causing leukocytes in the urine.

Kidney Infection

When an urinary tract infection is left untreated, an infection of the kidneys can develop. Also known as pyelonephritis, this infection can cause leukocytes in the urine. It is sometimes accompanied by a high fever and lower back or side pain as well as nausea and vomiting. Pyelonephritis should be treated immediately with antibiotics to prevent possible preterm labor and premature rupture of membranes. Pyelonephritis is the leading cause of hospital admission in pregnant women.

Asymptomatic Bacteriuria

Pregnant women may develop bacteria in their urinary tract and have no symptoms. This condition -- affecting between 2 to 10 percent of pregnant women -- is known as asymptomatic bacteriuria. Bacteria present in the urinary tract can cause leukocytes in the urine, and may lead to pyelonephritis if not treated properly with antibiotic therapy. Asymptomatic bacteriuria is the reason many offices routinely test the urine of all pregnant women.


Leukocytes can also appear in the urine during pregnancy if vaginal secretions become mixed with urine at the time the sample is collected. Secretions increase during pregnancy to keep the vaginal environment clean and free from bacteria. Pregnant women should cleanse the area with a hygienic wipe, from front to back, and avoid touching the cup to the vagina during collection to avoid mixing vaginal secretions with the urine.

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