711: Predicting recurrent spontaneous preterm birth in women with normal mid-trimester cervical length

Abstract

Spontaneous preterm birth (SPTB) remains the leading cause of morbidity and mortality among non-anomalous infants. Though a prior SPTB is the greatest risk factor for recurrence, and risk increases substantially with short cervical length (CL, <2.50cm), pregnancy outcomes are less certain among those with a normal CL. We sought to characterize risk factors for recurrent PTB in women with a normal mid-trimester CL. This is a secondary analysis of two prospective, multicenter studies that enrolled women with singleton gestations and ≥1 prior SPTB 15-36 weeks; study #1 was observational and study #2 was a RCT with negative findings (intervention did not impact SPTB rate). We included women with ≥ 1 vaginal CL 15.0-24.0 weeks’ with a shortest CL ≥ 25mm. We excluded those whose neonates were diagnosed with a major congenital anomaly postnatally. Women with recurrent PTB <37.0 weeks were compared to those delivering at term. Data were analyzed with chi-square, fisher’s exact, t-test, and stepwise backwards elimination logistic regression as appropriate. Of 521 women with ≥ 1 CL, 451 (87%) had a shortest CL ≥25mm and were included. Of these, 163 (35%) delivered preterm (median 34.4, IQR 31.0-36.0 weeks), and 288 (65%) delivered at term (median 38.9, IQR 37.9-39.7 weeks). Further, 72 (16%) delivered <32 weeks, including 29 (6%) <28 weeks. Demographic and baseline characteristics of those with PTB and term delivery are shown in Table 1. Those destined to have recurrent PTB had shorter ‘shortest’ CL [median 34mm (IQR 31,40) vs. 37mm (IQR 33,41) but were not more likely to have a shortest CL measuring 25-29mm (14% vs. 13%). The cervical length was measured at a median 18.6 (IQR 17.4, 20.4) weeks, and 9 women had a cerclage placed; these were similar in PTB and term births. Those with recurrent PTB were more likely to develop a placental abruption (9% vs. 3%, p=0.003). In multivariable models, several factors remained associated with recurrent PTB <37 weeks’ gestation (Table 2). The majority of women with a previous SPTB have a normal CL ≥25mm in the mid-trimester. Despite this, they remain at high risk for recurrent SPTB. Clinicians should remain vigilant when caring for women with a prior SPTB, even when the cervical length exceeds current intervention thresholds.View Large Image Figure ViewerDownload Hi-res image Download (PPT)