[Vaginal ultrasound study of the normal and incompetent cervix: attempting a mathematical assessment].

A group of 217 pregnant patients was examined by vaginosonography. The group could be divided into 62 patients with incompetent cervix and 155 patients with normal findings. We measured the width of the internal os, the length and the thickness of cervix of all patients in intervals of 14 days. We registered a dynamic process pattern of cervical, morphological changes in the group with preterm delivery. We tried to reduce these cervical changes to an arithmetic formula.