Gestational age-based reference ranges for cervical length and preterm birth prediction in triplet pregnancies: an observational retrospective study

Objectives To develop gestational age-based reference ranges for cervical length in triplet pregnancies. The secondary objective was to assess the performance of cervical length measured between 18 and 20 + 6 days for the prediction of preterm delivery before 28 and 32 weeks, respectively. Methods Observational retrospective study of triplet pregnancies in three Spanish tertiary-care hospitals between 2001 and 2019. Cervical length measurements were consecutively obtained between 15 and 34 weeks of gestation. Pregnancies undergoing multifetal reduction or fetal surgery were excluded. Results Two hundred and six triplet pregnancies were included in the final analysis. There was a quadratic decrease in cervical length with gestational age. The median and fifth centiles for cervical length at 20 weeks were 35 and 13 mm. In the prediction of preterm birth < 28 weeks, for a false positive rate of 5%, and 10%, the detection rates were 40.9%, and 40.9%, respectively, and the prediction of preterm birth < 32 weeks, 22.0% and 26.0%, respectively. Conclusions In triplet pregnancies, cervical length decreases with gestational age. The performance of cervical length at 18-20 + 6 in screening for preterm birth before 28 and 32 weeks is poor.