Expectant management in pregnancies complicated by previable preterm PROM between 20 and 23 6/7 weeks of gestation is associated with an overall neonatal survival rate of 49.0%, high risk of short- and long-term severe morbidity among survivors, and carries considerable maternal risks.

Objective To determine whether serial measurements of cervical length can improve the prediction of preterm birth in asymptomatic women with twin gestations compared with a single measurement of cervical length at mid-gestation. Materials and Methods This was a retrospective cohort study of women with twin pregnancies followed in a tertiary medical center between 2012 and 2014. All participants underwent routine measurement of cervical length at mid-gestation and every 2–3 weeks thereafter until 28–32 weeks. For each patient, cervical length was determined at the following time periods: 18+0 to 21+6 weeks (Period 1, routine exam), 22+0 to 24+6 weeks (Period 2), 25+0 to 27+6 weeks (Period 3) and 28+0 to 32+0 weeks (Period 4). Measurements of cervical length at Periods 2–4 were analyzed in the form of either absolute length (in mm) or percent shortening relative to cervical length at Period 1. The performance of a stepwise algorithm that incorporates serial measurements of cervical length for the prediction of preterm birth was compared to that achieved with a single measurement of cervical length at Period 1. Results Overall 441 women with twin pregnancies who were eligible for the study underwent a total of 2,374 cervical length measurements. The association of a short cervix (<10th percentile) with preterm birth at <32 weeks persisted in each of the four periods of gestation [Odds ratio (95%-confidence interval): 7.2 (3.1–16.5), 15.3 (6.4–36.7), 10.3 (4.4–24.3) and 23.1(8.3–64.1), respectively]. Compared with a single measurement of cervical length at mid-gestation (Period 1), a stepwise algorithm integrating serial cervical length measurements from all four successive gestational age periods resulted in a significant increase in the area under the ROC curve (0.917 vs. 0.613, p<0.001). Similarly, when a target false positive rate of 5% was used, the same stepwise algorithm was associated with a higher detection rate (69% vs. 28%, p<0.001), higher positive likelihood ratio (14.54 vs. 5.12) and a lower negative likelihood ratio (0.32 vs. 0.76) for preterm birth at <32 weeks compared with a single measurement of cervical length at Period 1. Conclusions Integration of serial measurements of cervical length using a stepwise algorithm in asymptomatic women with twin gestations can improve the detection of women at risk of preterm birth. Prospective studies are needed to validate these findings, and to investigate whether improved risk assessment performance is sufficient to offset the additional costs associated with serial cervical length measurements.