Ultrasonic assessment of cervix in 'at risk' patients.

One hundred and fifteen women were considered to be at risk of cervical incompetence, judging from their previous history. They were scanned serially from the first trimester to 32 weeks of gestation. Of the 115, 75 women were found to have defective cervix, as assessed on the basis of its length, its overall width and the width of the cervical canal at the level of the internal cervical os, and herniation of the amniotic membrane, with or without fetal parts, into the cervical canal. Sixteen of the 75 women with ultrasonically diagnosed cervical incompetence aborted, 40 needed cervical cerclage, 24 gave birth premature (24 to 34 weeks). Of the 115 women, 40 did not have ultrasonic evidence of cervical incompetence and only one patient gave birth at 36 weeks' gestation, while 39 patients gave birth between 37 and 42 weeks. These 40 women would have had cervical cerclage on the basis of clinical history alone. Ultrasound is an objective method of diagnosing the incompetent cervix and also helps to avoid unnecessary cerclage operations on the basis of history alone.