Azithromycin to Improve Latency in Exam Indicated Cerclage Control Trial

Preterm birth (PTB) continues to be a leading cause of neonatal morbidity and mortality. The rate of spontaneous PTB (delivery before 37 weeks gestation) is one in ten pregnancies and a history of prior preterm birth remains a risk factor for recurrence. The pathophysiology of cervical insufficiency leading to PTB remains poorly understood.

While interventions for PTB prevention are limited, the American College of Obstetrics and Gynecology (ACOG) supports the use of cervical cerclage. A physical exam indicated cerclage may be placed in the setting of painless cervical dilation in the second trimester. The cerclage is believed to provide mechanical support to a weakened cervix and promote the cervical mucosal plug as a barrier to ascending infection.

While many aspects of cerclage use have been extensively studied, the use of antibiotics prior to placement remains under evaluated. While antibiotic use is recommended during cesarean section, preterm premature rupture of membranes (PPROM), and obstetric anal sphincter injuries (OASIS), ACOG currently does not recommend perioperative antibiotics or prophylactic tocolytics at the time of cerclage placement citing insufficient evidence.

Miller et al. performed a randomized controlled trial (RCT) showing an increased incidence of pregnancy prolongation by at least 28 days among women who received indomethacin and perioperative antibiotics in the setting of an exam indicated cerclage compared to those who received no perioperative medications (92.3% vs 62.5%, p=0.01). Participants in the experimental arm received cefazolin or clindamycin if they had a penicillin allergy. Cefazolin is a first generation cephalosporin that has activity against gram positive cocci and gram negative rods and is commonly used for surgical prophylaxis. Clindamycin is a protein synthesis inhibitor and covers gram positive organisms and anaerobic bacteria, making it an appropriate alternative in cases of penicillin allergy. The use of cefazolin specifically with indomethacin has been studied retrospectively and showed a significant improvement in gestational latency (adjusted relative risk [aRR] 1.21, 95% CI 1.05-1.40) and birth weight (+489.8 grams, 95% CI 64.6-915.0).

The use of prolonged azithromycin with cerclage has been studied in a prospective, non- randomized fashion. In this study, patients were given 500mg azithromycin for 3 days and this was repeated every 10 days until 34 weeks. Patients who received this regimen and a cerclage had lower PTB (65.7% vs 5.7%, p<0.001) and reduced immediate fetal mortality (37.1% vs 0%, p<0.001).

The aim of our study is to determine if the addition of azithromycin prior to exam indicated cerclage prolongs gestation. Azithromycin is a macrolide antibiotic that binds to the 50S subunit of the bacterial ribosome and inhibits transpeptidation. It is effective against a wide variety of bacteria, specifically mycoplasma which has been associated with preterm birth. Azithromycin is currently used in obstetrics for patients undergoing nonelective cesarean delivery and as part of latency antibiotics in the setting of PPROM.