Cervical length, cervical dilation, and gestational age at cerclage placement and the risk of preterm birth in women undergoing ultrasound or exam indicated Shirodkar cerclage

Abstract Background: Preterm birth is a major cause of neonatal morbidity and mortality in the USA. 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 in women with a history of preterm birth and in women with painless cervical dilation in the second trimester, though the degree of cervical shortening, dilation, or gestational age at cerclage placement are not consistently associated with the subsequent rate of preterm birth. Our objective was to determine if cervical length (CL), cervical dilation or gestational age (GA) at the time of cerclage placement are associated with preterm birth among women undergoing ultrasound-indicated or exam-indicated cerclage. Study design: This was a retrospective cohort study of all patients with a singleton pregnancy who underwent ultrasound-indicated or exam-indicated Shirodkar cerclage placement at a single maternal-fetal medicine practice in New York City between November 2005 and May 2017. All patients included in the study had previously undergone CL screening for an increased risk of preterm birth (for example, prior spontaneous preterm birth or mid-trimester loss, prior cervical excision). The cervical length or dilation 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 or ≥36 weeks. Planned subgroup analyses of the primary outcome were performed based on CL at the time of ultrasound-indicated cerclage (0–9 mm, 10–19 mm, ≥20 mm), cervical dilation at the time of physical exam-indicated cerclage (<2 cm vs. ≥2 cm), and gestational age at cerclage placement (<20 weeks vs. ≥20 weeks). Data were analyzed using the Student’s t-test and chi-square test for trend. Results: There were 123 and 39 patients in the ultrasound- and exam-indicated cerclage groups, respectively. Twenty six (21.2%) patients in the ultrasound-indicated subgroup and 24 patients (61.5%) in the exam-indicated subgroup delivered <36 weeks. CL (16.4 versus 17.6 mm, p = .28) and GA (19.7 versus 20.0 weeks, p = .58) at the time of ultrasound-indicated cerclage placement were not significantly different in patients who delivered <36 and ≥36 weeks’ gestation, respectively. Women with cervical dilation ≥2 cm prior to exam-indicated cerclage placement were significantly more likely to deliver <36 weeks when compared to women with cervical dilation <2 cm (77.8 versus 47.6%, p = .05); however, there were no significant differences in rates of preterm birth <28 and <32 weeks between these two groups (38.9 versus 23.8%, p = .31 and 50.0% versus 28.6%, p = .17, respectively). Conclusions: Cervical length and GA at the time of ultrasound-indicated Shirodkar cerclage placement do not appear to impact the likelihood of preterm birth <36 weeks, while cervical dilation ≥2 cm at the time of exam-indicated Shirodkar cerclage is associated with an increased rate of preterm birth <36 weeks, but not earlier gestational ages at delivery.