Optimal antenatal corticosteroid exposure in women with history of preterm birth and asymptomatic short cervical length

Abstract

A proposed benefit of cervical length assessment after 24 weeks' gestation in women with a history of preterm birth is to aid in the timing of antenatal corticosteroids in otherwise asymptomatic women. We sought to investigate whether the use of an ultrasonographic short cervical length as an indication for antenatal corticosteroids in asymptomatic women results in optimal exposure compared with women receiving antenatal corticosteroids for preterm labor symptoms. Retrospective cohort study of all women with a previous spontaneous preterm birth and a singleton gestation who underwent serial cervical length assessment at a large academic tertiary medical center from 2011 to 2016. Patients were included in the analysis if they received antenatal corticosteroids for either an asymptomatic short cervical length or symptoms of preterm labor. The primary outcome was optimal antenatal corticosteroids exposure (latency to delivery of ≤7 days). Poisson regression with robust error variance was used to calculate incidence rate ratios (IRR) and confidence intervals (CI) for primary and secondary outcomes adjusting for primary and secondary outcomes adjusting for race, earliest previous preterm birth, and current cerclage. There were 287 women meeting inclusion criteria, among whom 166 (57.8%) received antenatal corticosteroids for a short cervical length and 121 (42.2%) for preterm labor symptoms. Women who received antenatal corticosteroids for a short cervical length were less likely to have optimal exposure (1.2% vs 19.0%; incidence rate ratios, 0.06; confidence interval, 0.02-0.27) compared with women with preterm labor symptoms. They were also more likely to have exposure with eventual term delivery (43.2% vs 33.4%; incidence rate ratios, 1.6; confidence interval, 1.2-2.0). Importantly, women who received antenatal corticosteroids for a short cervical length were significantly less likely to receive either an initial or rescue antenatal corticosteroids course within 7 days of a preterm delivery of less than 34 weeks' gestation (42.9% vs 76.9%; incidence rate ratios, 0.52; confidence interval, 0.35-0.75). Women with a previous preterm birth who receive antenatal corticosteroids for an asymptomatic short cervical length are less likely to have optimal exposure than women with symptoms of preterm labor. These data challenge the practice of cervical length surveillance for the sole indication of timing antenatal corticosteroids administration.