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Second-trimester chlamydia infection is associated with an increased risk of subsequent preterm birth

Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen in the United States and is estimated to infect from 2 to 37 percent of pregnant women. Unfortunately, women with chlamydia infection during the second trimester of pregnancy are two to three times as likely as uninfected women to have a preterm birth, according to a recent study by the Patient Outcomes Research Team (PORT) on Low Birthweight in Minority and High-Risk Women. The PORT was led by Robert L. Goldenberg, M.D., of the University of Alabama at Birmingham and supported by the Agency for Healthcare Research and Quality (PORT Contract 290-92-0055).

The researchers compared results of a sensitive DNA test for chlamydia on stored urine specimens collected at 24, 26, 28, and 30 weeks' gestation for women who had a preterm birth at less than 37 weeks' gestation with specimens from women who delivered at term. Chlamydia infection (11 percent overall) was nearly three times more common at 24 weeks' gestation (16 vs. 6 percent) but not at 28 weeks (13 vs. 11 percent) among women who gave birth prematurely compared with women who delivered at term. After adjustment for other risk factors for preterm birth, women with chlamydia infection at 24 weeks' gestation were twice as likely as uninfected women to have a preterm birth at less than 37 weeks' gestation and three times as likely to have a preterm birth at less than 35 weeks' gestation.

Chlamydia infection was significantly more common among women with certain risk factors for preterm birth, such as bacterial vaginosis (57 vs. 33 percent) and a short cervical length (33 vs. 18 percent), but it is not clear whether preterm birth is mediated through these factors. Also, whether universal screening with a DNA test and subsequent treatment for chlamydia infection, as used in this study, would significantly reduce spontaneous preterm delivery remains an unanswered question. The frequency of preterm birth in the United States has increased during recent years despite the recommendation of the Centers for Disease Control and Prevention for chlamydia infection screening among pregnant women.

See "The preterm prediction study: Association of second-trimester genitourinary chlamydia infection with subsequent spontaneous preterm birth," by William W. Andrews, Ph.D., M.D., Dr. Goldenberg, Brian Mercer, M.D., and others, in the September 2000 American Journal of Obstetrics & Gynecology 183, pp. 662-668.

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