Azithromycin treatment for short cervix with or without amniotic fluid sludge: A matched cohort study

Preterm birth (PTB) is one of the leading causes of neonatal mortality and morbidity worldwide. A shortened cervix is a recognised risk factor for PTB, and amniotic fluid sludge (AFS) diagnosed on ultrasound may be suggestive of underlying inflammation or infection.

The aim is to determine if azithromycin, administered in cases of a shortened cervix, results in prolongation of gestation with improvements in neonatal outcomes.

We performed a retrospective cohort study at three tertiary maternity services in Melbourne, Australia, between 2015 and 2020. Women with a singleton pregnancy were included if they had a cervical length of 15 mm or less at 13-24 weeks' gestation, with or without AFS. Exclusion criteria comprised multiple pregnancy, major fetal congenital anomaly, placenta praevia, prelabour premature rupture of membranes, vaginal bleeding and/or clinical signs suggestive of chorioamnionitis at the time of diagnosis of the short cervix. The results of antibiotic treatment with azithromycin were compared to those of no antibiotic treatment. The outcomes of interest were PTB, prelabour premature rupture of membranes (PPROM), chorioamnionitis and neonatal morbidity.

A total of 374 women were included in the study, of whom 129 received azithromycin and 245 received no antibiotics. When adjusting for potential confounders, the adjusted risk of PTB overall was higher in the treatment group (adjusted hazard ratio 1.36 (95% confidence interval 1.04-1.77) P = 0.023) with no differences found for PPROM, chorioamnionitis or neonatal morbidity.

These data do not support the routine use of azithromycin in women with a short cervix, including those with AFS detected on ultrasound.