Microbiology of the lower genital tract and amniotic fluid in asymptomatic preterm patients with intact membranes and moderate to advanced degrees of cervical effacement and dilation.

The purpose of this prospective investigation was to evaluate the microbiology of the lower genital tract and amniotic fluid in asymptomatic women with preterm labor. We limited inclusion in the study to patients at 20 to 36 weeks' gestation whose membranes were intact and whose cervix was at least 50% effaced and 2 cm dilated. At the time of admission, we obtained an endocervical specimen for culture for Neisseria gonorrhoeae and for enzyme-linked immunoabsorbent assay for Chlamydia trachomatis and a vaginal specimen for culture for group B streptococci (GBS). We also performed transabdominal amniocentesis to collect amniotic fluid for Gram's stain, latex fixation test for GBS, and aerobic and anaerobic cultures. All patients received parenteral tocolytics. Women who had an immature lecithin to sphingomyelin ratio also received betamethasone. Only 1 of 72 women (1.4%, 95% confidence interval 0 to 4.1%) had a positive amniotic fluid culture. One patient (1.4%) had a positive Gram's stain, and two (2.8%) had positive latex fixation tests. None of these individuals subsequently had a positive culture. Eight women (11.1%) had positive tests for chlamydia, and four (5.5%) had positive vaginal cultures for GBS. None of the patients developed clinical evidence of chorioamnionitis, and only one had puerperal endometritis. None of the neonates had any complications due to infection. We conclude that, in our population, intra-amniotic infection is not a common cause of preterm labor in asymptomatic patients with intact membranes and that amniocentesis should not be performed routinely to assess the bacteriology of the amniotic fluid.