Congenital incompetence of the cervical os: reduction of bulging membranes with a modified Foley catheter.

A case is described of congenital incompetence of the cervix associated with pronounced bulging of the fetal membranes through the cervical os. The patient, a primigravida, presented at 25 weeks' gestation without any evidence of uterine activity. She had no past history of cervical surgery or disease. The tip beyond the bulb of a size 22 Foley catheter was removed. We inflated the bulb progressively while applying sustained, gentle pressure to the bag of forewaters. Upon reducing the membranes to within the uterine cavity, we inflated the bulb of the catheter further with saline to a total volume of 25 cc. This procedure maintained the catheter within the uterine cavity and facilitated the insertion of a MacDonald cerclage in the region of the internal cervical os.