Sonographic appearance of the uterine cervix in pregnancy: the vertical cervix

The uterine cervix, internal os, and endocervical canal can be accurately identified in pregnant women without distortion when the maternal bladder is empty. The internal os may vary in appearance from a flat to a very slightly funneled shape; a protuberance at the internal os is a variant of normal. In a series of 50 consecutive patients, the cervix was well visualized in 30. With the maternal bladder empty, it was clearly seen in all patients of less than 20 weeks gestation, in 13 of 19 patients at 20-30 weeks gestation, and in three of 17 patients at 30-40 weeks gestation. The mean length of the cervix was 3.25 cm with no difference between primagravida and multigravida patients. When the bladder was partially filled, the mean length of the region of the cervix was 4.6 cm which was significantly greater than with the bladder empty. This suggests that even partial filling of the bladder distorts the appearance of the cervix.