[Early diagnosis of the cervical incompetency by the ultrasonography].

To establish a reliable method for diagnosing cervical incompetency, we observed changes in the cervix by ultrasonography and tried to settle the criteria for early diagnosis. The ultrasonographic evaluation of the cervix was performed by real time B mode scanning (Aloka Echo camera SSD 650 with attached sector scanner using 3.5 MHZ transducers). The cervical length was defined as the distance from the lower edge of the fetal membranes to the edge of the portio vaginalis. In the case of normal pregnancy, the cervical length increased gradually from 14 to 24 weeks of gestation and then decreased gradually. In the case of patients who delivered before 33 weeks of gestation, the cervical length was less than -ISD. 78 of 79 cases in whom bulging of the membranes was not seen delivered at term, but 9 of 33 cases with bulging membranes delivered preterm (chi2, p less than 0.001). The criteria of cervical incompetency based on ultrasonographic findings are as follows: 1. Bulging of the fetal membranes into the endocervical canal 2. Shortening of the cervix a. the cervical length less than -ISD of the mean value b. the decrease in cervical length before 24 weeks of gestation