Cervical Dilation

A cause of miscarriage and preterm birth in the second and third trimesters, cervical incompetence is a condition in which the cervix begins to open (dilate) and thin (efface) before a pregnancy has reached term. In a woman with cervical incompetence, dilation and effacement of the cervix occur without pain or uterine contractions. Instead of happening in response to uterine contractions, as in a normal pregnancy, these events occur because of a weakness in the cervix, which opens under the growing pressure of the uterus as pregnancy progresses. If the changes are not halted, rupture of the membranes and birth of a premature baby can result.

If you have an incompetent cervix, the medical name for this condition may give you the impression that you are somehow faulty, inadequate, or weak. This is not the case — “incompetent” in this sense simply means that the muscle of the cervix is not able to withstand the pressure of the uterus. Because you cannot voluntarily control this muscle, it cannot possibly be due to any failure on your part.

What causes it and who's at risk? Cervical incompetence is relatively rare, occurring in only 1 to 2 percent of all pregnancies. It is thought to cause as many as 20 to 25 percent of miscarriages in the second trimester. It may have any of several possible causes, such as:

* A previous operation on the cervix (D&C or biopsy)
* Damage to the cervix during a prior difficult delivery
* A malformation in the cervix due to a birth defect (such as in DES-exposed women).

These risk factors make it more likely for the problem to recur in another pregnancy. Other women at risk for this problem include those who are pregnant with more than one fetus and those who have an excess of amniotic fluid (a condition called hydramnios) in the current pregnancy. For these women, cervical incompetence is less likely to recur in a subsequent pregnancy.

What are the symptoms? Cervical incompetence may cause some of the typical symptoms of miscarriage or preterm labor. When the following signs or symptoms occur in the absence of abdominal pain, cervical incompetence may be the cause:

* Spotting or bleeding
* A vaginal discharge that is bloody or thick and mucus-like (the latter may be the passing of the mucus plug from the cervix)
* A sensation of pressure in the lower abdomen

You need to be especially alert to these signs if you had a miscarriage or preterm labor in a previous pregnancy which was due to cervical incompetence.

How is it diagnosed? Some attempts have been made to diagnose cervical incompetence before it causes problems, but these efforts have not been very successful.

What's the treatment? If you were diagnosed with cervical incompetence in a previous pregnancy, your doctor might take steps to prevent the problem from recurring in this pregnancy. Treatment may include cerclage, a surgical technique to reinforce the cervical muscle. Several procedures are used for cerclage, but they all involve placing sutures above the opening of the cervix to narrow the cervical canal.

Cerclage is most successful if it is performed relatively early in pregnancy by about 18 or 20 weeks. Depending on what type of procedure was used, the sutures may either stay in place or be removed close to your due date. Placement of a cervical cerclage does not completely protect a woman from miscarriage or preterm delivery. Additional treatment, such as bed rest or tocolytic therapy (medication to stop uterine contractions), may also be needed. Even with a cerclage and additional therapy, the risk of preterm birth is high (about 25 percent in some studies) in women with cervical incompetence.