Forces required for dilatation of human cervix in first trimester of pregnancy.

Cervical resistance to dilatation was measured in 76 patients undergoing first trimester legal abortion; a specially designed force-sensing instrument was used. No correlation between cervical resistance and patient age or gestational age was found. Increasing parity and earlier legal abortions were significantly correlated with a lowering of the cervical resistance. In patients dilated to 11 mm a lowering of resistance was noted suggesting a tear in cervical tissue.