NEW YORK (Reuters Health) – Screening pregnant women for chlamydia using urine samples is just as accurate as when cervical secretions are used, suggests a new study published in Obstetrics and Gynecology.

Urine sampling is also considerably cheaper than endocervical sampling — and scores points with patients who would rather not undergo an invasive exam.

The comparison was done by Dr. Scott Roberts and his colleagues at the University of Texas Southwestern Medical Center in Dallas. For 4 months, all women who were seen at a group of family planning and obstetric complication clinics in the area who were between 35 and 37 weeks pregnant were tested for Chlamydia trachomatis using both methods.

A total of 2,018 pregnant women were tested. The population was a mean 26.9 years old, and was 84% Hispanic.

Samples were analyzed using the Aptima Combo 2 Assay.

The prevalence of chlamydia according to tests of cervical secretions was 4.3% (95% CI: 3.4-5.2%), compared to 4.1% using urine sampling (95% CI: 3.3-5.1%). McNemar’s test found the results to be concordant, and the K estimate of 0.982 (95% CI: 0.961-1.000) was in the range “considered almost perfect.”

Sensitivity of urine screening was 96.5% relative to endocervical screening (95% CI: 90.1-99.3%), with a relative specificity of 100% (95% CI: 99.8-100%).

Chlamydia screening for pregnant women is recommended by the Centers for Disease Control and Prevention, the American College of Obstetricians and Gynecologists, and the U.S. Public Health Service.

While urine screening for chlamydia has shown to be accurate in male and non-pregnant female populations, Roberts and his colleagues weren’t positive that would translate to effectiveness in pregnant women.

“Our concern was that pregnant women may have amplification inhibitors not present in the nonpregnant population leading to nucleic acid amplification tests being less sensitive when performed on urine as compared with cervical specimens,” they write. That was not the case, however.

Previous studies have suggested that testing for chlamydia using urine samples may cut almost half the cost off endocervical testing.

The authors conclude, “Removing the need for a speculum examination with its potential benefits in costs and respect for patients’ desires has led us to use urine nucleic acid amplification testing for our C trachomatis screening in all pregnant women at our institution.”

Ob Gynecol