Cervical changes throughout pregnancy as assessed by transvaginal sonography

To evaluate changes in cervical dimensions by transvaginal ultrasound in non-randomly selected pregnant women.

This longitudinal study included 154 pregnant women undergoing transvaginal ultrasound assessment of the cervix at a mean gestational age of 12, 16, 20, 25, and 31 weeks. On each occasion, the longitudinal and anteroposterior diameters of the cervix were measured. The rate of prematurity in the series was 1.9%, and the mean gestational age at delivery was 38.7 weeks.

Overall, cervical length (mean 4.3 cm; 95% confidence interval 4.1-4.3) did not change significantly (P = .06), whereas the 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 did not correlate with cervical dimensions at any stage of pregnancy.

The cervix undergoes a change in shape from cylindrical to conic, more marked in primigravidas than in parous women. Women who had previous cesarean deliveries had cervical characteristics similar to primigravidas; therefore, it appears that mechanical, rather than hormonal, factors have a greater effect in determining changes of cervical dimensions throughout pregnancy.