[Assessment of the caliber of the uterine isthmus at the beginning of pregnancy. Its value in the indication for cervical cerclage. 134 cases].

In capable hands, measurement of the uterine isthmus in early pregnancy is without danger. Apparent incompetence of the isthmus as determined by examination other than during pregnancy or a previous cervical cerclage do not necessarily represent a formal indication for a cerclage in a subsequent pregnancy. Calibration of the isthmus during pregnancy was carried out in 129 patients who were "candidates" for a cerclage. It was possible to avoid the procedure in 80 of them, i.e. 62% of cases. Furthermore no risk to the pregnancy was involved. Since beginning this study, the number of cervical cerclages in our department has decreased and we have observed a parallel decrease in premature deliveries, since with the elimination of problems related to the isthmus we have directed our efforts towards other causes of premature labour. Thus we have been led to include calibration of the isthmus in routine examinations in pregnancies occurring on the one hand in women with previous infertility as well as in those in which pregnancy follows a period of involuntary sterility. Calibration reveals early incompetence of the isthmus, making cerclage possible at the appropriate time.