An incompetent cervix is an inability of the cervix to remain closed. It may be a mechanical defect in the cervix which causes the cervical os to dilate prematurely during the mid-trimester of pregnancy. This premature dilating results in spontaneous abortion or preterm labor. Incompetent cervix may be caused by congenital anomalies of the uterus, cervix, prior cervical trauma, DES exposure, hormonal influences, congenitally short cervix, or uterine anomalies. The symptoms include painless dilatation, presence of bloody show, and bulging membranes.

The diagnosis of incompetent cervix is usually made when a second trimester pregnancy is lost with a sudden unexpected rupture of the membranes followed by painless expulsion of the fetus. When this repeated history of incompetent cervix is due to an anatomical factor, surgical treatment known as cerclage (suturing the cervix) may be performed to prevent relaxation and dilation of the cervix. A modified Shirodkar technique or the McDonald technique are the most commonly used techniques.

With the Shirodkar technique, the vaginal mucosa membrane is elevated. A band of homologous fascia or narrow band of some material such as Mersilene is wrapped around the internal os and tied. The vaginal mucosa is then restored to its original position and sutured. With the McDonald technique, a simpler procedure, a non-absorbable suture in placed around the cervix high on the cervical mucosa. A cerclage may be done at 12-14 weeks gestation. Success rates with cerclage are approximately 80-90%.

After the cerclage, concerns include monitoring fetal heart rate and watching for signs of rupture of the membranes or uterine contractions. If the membranes rupture, the cerclage is removed and the uterus is usually emptied because of the risk of infection. Sometimes, increased doses of antibiotics are used after the SROM (spontaneous rupture of membranes) to maintain the pregnancy. If contractions begin, the client should be placed on bedrest and a tocolytic agent such as ritodrine hydrochloride may be given in an effort to control the contractions.

When the cerclage is present and the pregnancy continues successfully, the cerclage is usually removed after the 37th week of gestation. This may be followed by the onset of labor and a rapid delivery. In some situations, cesarean delivery may be elected to preserve the suture for future pregnancies.