Early cervical length, preterm prelabor and gestational age at delivery. Is there a relationship?

To measure early cervical length by transvaginal ultrasound in the late first trimester, to examine its relationship to the occurrence of preterm prelabor diagnosis and to relate both to gestational age at delivery.

In a cohort of 373 women with singleton pregnancies, early cervical length was measured transvaginally at the time of a routine dating ultrasound examination (11.3 +/- 1.9 weeks gestation). For measurements < 40 mm the cervix was remeasured by 20 weeks' gestation; measurements > or = 40 mm were recorded but not used. Beginning at 20 weeks' gestation, all patients were regularly questioned, as part of normal prenatal care, for symptoms consistent with preterm cervical effacement with or without increased uterine activity.

Early cervical length at or below the 10th percentile (40 mm) was significantly associated with an increased relative risk of preterm prelabor (P < .0001). Preterm prelabor diagnosis was significantly associated with earlier median gestational age at delivery: 38.7 vs. 39.9 weeks (P < .0001 by Wilcoxon-Mann-Whitney analysis). Kaplan-Meier survival analysis for gestational age at delivery was also significant (P < .0001).

Measuring of cervical length in the late first trimester predicts the risk of preterm prelabor, and women with preterm prelabor deliver earlier that those without.