Serial versus once-only cervical length screening in twin pregnancies

Objective: To assess the impact of serial versus once-only transvaginal ultrasound (TVU) cervical length (CL) screening in twin pregnancies. Study Design: Multicenter retrospective cohort study including twin pregnancies who underwent TVU CL screening from 16 0/7-23 6/7 weeks of gestation between 2017 and 2022. Twin pregnancies resulting from multifetal pregnancy reduction after 14 weeks of gestation, monochorionic monoamniotic twins, and those undergoing a history-indicated cerclage were excluded. Cases were stratified into two groups based on number of TVU CL assessments: twins who had more than one CL assessment from 16 0/7-23 6/7 weeks’ gestation (i.e. serial CL group) versus twins who had only one CL assessment at the time of their detailed fetal anatomy ultrasound from 18 0/7-21 6/7 weeks’ gestation (i.e. once-only CL group). Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of CL screening for predicting preterm birth (PTB) at various gestational age cut-offs (<34, <32, and <28 weeks of gestation) were calculated using thresholds of both ≤25 mm and ≤30 mm and compared between the two groups. Statistical significance was set at P < 0.05. Results: Of the 1,917 patients included, 962 (50.2%) were in the serial CL group and 955 (49.8%) were in the once-only CL group. The incidence of a short CL ≤25 mm was significantly higher in the serial CL group compared to the once-only CL group (12.6% vs. 0.9%, P <0.001). The sensitivity of CL screening for predicting PTB, when using a threshold of ≤25 mm, was higher in the serial CL group compared to the once-only CL group for each PTB cut-off (<34 weeks: 27.9% vs. 4.2%; <32 weeks: 40.7% vs. 7.4%; <28 weeks: 47.2% vs. 11.8%, respectively). Conclusion: Serial TVU CL screening from 16 0/7 - 23 6/7 weeks of gestation should be considered in twin pregnancies.