ABSTRACT
A nomogram of cervical dimensions during normal pregnancy was established by prospective longitudinal comparative study of total 304 gravida in two groups : normal group [n=204] and high riskgroup [n=100] with clinical diagnosis of cervical incompetence. Normal cases were evaluated by TVS from 10th week to 38th week of pregnancy, high risk cases before and after cerclage,onward till delivery. The mean, standard deviation, minimum, maximum, range, and cut off values for each of the following 5 cervical parameters were obtained: cervical length, internal os diameter, thickness of lower uterine segment, posterior cervical angle and cervical thickness. By discriminant analysis of values for normal pregnant and those for high risk pregnant cases, we derived our sonographic criteria for diagnosis of incompetent cervix which include: cervical length < 25 mm internal os diameter > 6 mm, and posterior cervical angle > 90°. These variables can predict cervical incompetence correctly in 86.4% and exclude it in 88.9% of cases