Vaginal ultrasonographic assessment of cervical length changes during normal pregnancy.

We measured the cervical length of 166 normal, gravid patients between 8 and 37 weeks' gestation by vaginal ultrasonography. Patients were assigned to one of five groups according to gestational age at the time of the measurements. Cervical length was longest (48 mm) in group 3 (20 to 25 weeks) and significantly longer than that of groups 1 (8 to 13 weeks), 2 (14 to 19 weeks), and 5 (32 to 37 weeks). The use of vaginal ultrasonography to assess cervical length eliminates some technical problems encountered with abdominal ultrasonography. Nomogram of cervical length throughout pregnancy was established. This may aid in early diagnosis and management of preterm labor and cervical incompetence.