Does 17a-Hydroxyprogesterone Caproate for Preterm Birth Prevention Affect Midtrimester Cervical Length? [37F

Abstract

INTRODUCTION: Weekly intramuscular 17a-hydroxyprogesterone caproate (17P) is endorsed by the American College of Obstetricians and Gynecologists for recurrent preterm birth (PTB) prevention. Cerclage is indicated in patients with prior PTB and a midtrimester cervical length (CL) less than 25 mm. While 17P and CL screening are used concurrently in this population, 17P’s effect on CL is unclear. As such, we aimed to investigate the effect of 17P on midtrimester CL in patients with prior PTB. METHODS: Retrospective cohort of all singletons delivered at a single center that underwent CL screening from 2011 to 2016 for prior PTB. Exposure was defined as at least one dose of 17P administered prior to the last measured CL. Primary outcome was shortest observed CL. Secondary outcomes included rate of CL shortening to less than 25 mm and cerclage. ANCOVA was used to assess the relationship between 17P and shortest observed CL, controlling for significant covariates. RESULTS: Of 409 women who had CL screening, 211 received and 198 did not receive 17P prior to the last CL. Exposed and unexposed groups differed by initial CL (38.3 vs 36.0 mm, respectively; P < .005) and gestational age of earliest prior PTB (27.1 vs 29.2 weeks, respectively; P < .001). Rates of CL shortening to less than 25 mm (P = .93) and cerclage (P = .471) were similar. After controlling for confounders, shortest observed CL was significantly shorter in those who received 17P prior to the last CL (30.2 vs 32.7 mm; P < .001). CONCLUSION: 17P does not prevent midtrimester CL shortening in patients with prior PTB.