533: Ultrasound-indicated cerclage: Does the actual cervical length or gestational age matter?

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In many patients at risk for preterm birth, cervical length (CL) screening is used to guide decisions regarding cerclage placement. Quality evidence shows that cerclage prolongs pregnancy in high-risk women with a short CL. However, it is unknown if the actual CL measurement or gestational age (GA) at cerclage placement are associated with preterm birth. Our objective was to determine if CL and GA at the time of ultrasound-indicated cerclage placement are associated with preterm birth. This was a retrospective cohort study of all patients who underwent ultrasound-indicated cerclage placement at a single maternal-fetal medicine practice in New York City between 11/2005 and 5/2017. All patients underwent CL screening for an increased risk of preterm birth (prior preterm birth, prior midtrimester loss, or history of LEEP). All cerclages were of the Shirodkar type. Cervical length and GA at the time of cerclage placement were collected, as were demographic and obstetric outcome data for the current pregnancy. The primary outcome was delivery <36 weeks, as cerclages were typically removed between 36-37 weeks. Data were analyzed using the Student’s t-test and Chi-square test for trend. There were 123 patients identified who underwent ultrasound-indicated cerclage, 26 (21.2%) of whom delivered <36 weeks. Cervical length (16.4 vs. 17.6 mm, p=0.28) and GA (19.7 vs. 20.0 weeks, p=0.58) at the time of cerclage placement were similar in patients who delivered <36 and >36 weeks’ gestation, respectively. When stratified by CL prior to cerclage placement, there was no significant difference in rates of preterm birth <28, <32, and <36 weeks (Table). Cerclage placement <20 weeks’ vs. >20 weeks’ gestation also did not significantly impact the rate of preterm birth. Cervical length and gestational age at the time of ultrasound-indicated cerclage placement do not appear to impact the likelihood of preterm birth <36 weeks. Patients should be reassured that outcomes are similar regardless of the CL or GA prior to cerclage placement.