Postpartum cervical length as a predictor of subsequent preterm birth-novel insights on an old enigma

Preterm birth poses one of the biggest challenge in modern obstetrics. Prediction of preterm birth has previously been based on patient history of preterm birth, short cervical length around midtrimester, and additional maternal risk factors. Little is known about cervical length and physiology during the postpartum period and any associations between postpartum cervical features and subsequent preterm birth.

This study aimed to determine the feasibility and utility of postpartum cervical length measurements in prediction of subsequent spontaneous preterm birth.

This was a prospective cohort study in a single tertiary center, conducted during a 5-year period (2017-2021). We evaluated the mean postpartum cervical length in patients after both preterm birth and term deliveries at 4 time periods: 8, 24, and 48 hours, and 6 weeks postpartum, with follow-up in their subsequent pregnancies to evaluate gestational age at delivery. The mean postpartum cervical length in different populations stratified by gestational age at delivery was assessed in phase 1 of the study, and the gestational age at subsequent delivery was assessed in phase 2.

A total of 1384 patients participated in phase 1. Mean postpartum cervical length was significantly shorter in the preterm birth (<34 weeks' gestation) group than in the term group at 8 hours (8.4±4.2 vs 22.3±3.5 mm; P<.0001), 24 hours (13.2±3.8 vs 33.2±3.1 mm; P<.0001), and 48 hours (17.9±4.4 vs 40.2±4.2 mm; P<.0001) postpartum. There was no significant difference in mean postpartum cervical length between the preterm birth group and the term group at 8, 24, and 48 hours postpartum. Cervical length was similar between the groups at 6 weeks postpartum. A total of 891 patients participated in phase 2. The area under the curve was higher for preterm birth screening based on a history of a short postpartum cervix alone than for a history of spontaneous preterm birth alone (0.66 [95% confidence interval, 0.63-0.69] vs 0.57 [95% confidence interval, 0.54-0.61]; P<.0001). Combining both a history of spontaneous preterm birth and a short postpartum cervix resulted in additional benefit, with an area under the curve of 0.74 (95% confidence interval, 0.73-0.84; P<.0001).

Postpartum cervical length measurements may assist in detecting the group of patients at higher risk of subsequent spontaneous preterm birth. It may be beneficial to consider an increased follow-up regimen and earlier interventions in this group to reduce adverse perinatal outcomes.