Predictive value of a short cervix in the early third trimester for preterm birth in twin pregnancies

Preterm birth (PTB) is a major cause of neonatal morbidity and mortality, and cervical length measured in the mid-trimester is a well-established predictor of PTB. However, the predictive value of cervical length in the early third trimester remains unclear, particularly in twin pregnancies. This study aimed to investigate the association between a short cervical length (≤ 25 mm) measured during the early third trimester (28 + 0 to 33 + 6 weeks) and the risk of PTB before 37 weeks, and to evaluate its predictive utility.

This retrospective cohort study included women with twin pregnancies who delivered at a single tertiary hospital between 2009 and 2019. Women with a history of cervical cerclage, iatrogenic preterm birth, or missing cervical length measurements in the second or early third trimester were excluded. Participants were categorized into short cervix and control groups based on cervical length in the early third trimester.

Among 291 twin pregnancies, 102 (35.1%) resulted in PTB. The incidence of PTB was significantly greater in the short cervix group (73.0%) compared to the control group (29.0%, P < 0.001). A short cervix in the early third trimester was associated with a 3.7-fold increased risk of PTB. Among women with a normal cervical length in the second trimester, those with cervical shortening in the early third trimester had a 2.3-fold increased risk. Incorporating third-trimester cervical length improved PTB risk prediction, increasing the area under the receiver operating characteristic curve from 0.629 to 0.711 (P = 0.001).

A short cervical length in the early third trimester is associated with an increased risk of PTB in twin pregnancies. Assessing cervical length during this period may improve risk stratification and inform clinical assessment, particularly among asymptomatic or relatively lower-risk populations.