CERVICAL CHANGES THROUGHOUT PREGNANCY AS ASSESSED BY TRANSVAGINAL SONOGRAPHY

Objective: To evaluate changes in cervical dimensions by transvaginal ultrasound in non-randomly selected pregnant women. Methods: This long itudinal study included 154 pregnant women undergoing transvaginal ult rasound assessment of the cervix at a mean gestational age of 12, 16, 20, 25, and 31 weeks. On each occasion, the longitudinal and anteropos terior diameters of the cenix were measured. The rate of prematurity i n the series was 1.9%, and the mean gestational age at delivery was 38 .7 weeks. Results: Overall, cervical length (mean 4.3 cm; 95% confiden ce interval 4.1-4.3) did not change significantly (P = .06), whereas t he anteroposterior diameter of the cervix at its midportion shortened throughout the investigated period of gestation. Multiparous women had longer and thicker cervices than primigravidas or women with previous cesareans or first-trimester abortions. Gestational age at delivery d id not correlate with cervical dimensions at any stage of pregnancy. C onclusions: The cervix undergoes a change in shape from cylindrical to conic, more marked in primigravidas than in parous women. Women who h ad previous cesarean deliveries had cervical characteristics similar t o primigravidas; therefore, it appears that mechanical, rather than ho rmonal, factors have a greater effect in determining changes of cervic al dimensions throughout pregnancy.