Incompetent Cervix, Now What?

October 5th, 2009

One of the most common indications for the bed rest prescription is incompetent cervix. What is an incompetent cervix and what does it mean for the pregnancy if a woman has this diagnosis?

Simply put, an incompetent pregnancy is one that is unable to remain closed for a full term pregnancy. Abnormally weak, an incompetent cervix will gradually widen (dilate) and shrink (efface) typically during the second trimester of pregnancy as the uterus enlarges and becomes heavier. Undiagnosed, incompetent cervix often leads premature labor and/or miscarriage.

There are several causes for incompetent cervix. These include:

  • Congenital abnormalities
  • Hormonal changes such as occur during pregnancy
  • prior cervical surgery (such as conization)
  • Trauma during another procedure (such as during dilation for D&C) or a prior traumatic delivery
  • In Utero Exposure to DES (Diethylstilbestrol)
  • No obvious reason

Unfortunately for many women, the first indication that they have an incompetent cervix is when preterm labor or a miscarriage occurs. With subsequent pregnancies these ladies may opt to have a cerclage, a surgical procedure during which the cervix is stitched closed, performed between about 14-16 weeks gestation. Depending on the woman’s situation, she may then be prescribed bed rest for the remainder of her pregnancy.

For some women, the incompetent cervix is not initially detected, but becomes suspect if a women has 3 consecutive pregnancy losses in the second trimester.  Pregnancy loss due to incompetent cervix occurs in about 20-25% of all second trimester pregnancy losses. An incompetent cervix can be detected via manual examination or by ultrasound.

Once an incompetent cervix is diagnosed, what then? For those ladies in whom there is no anatomic abnormality, the cerclage will typically suffice. If the cervix is too dilated (more then 4 cm) or if there are complications with the fetus (intrauterine fetal demise, premature rupture of membranes (rupture of the amniotic sac) then a cerclage cannot be performed and the pregnancy will be lost. But of the cervix is less than 3 cm dilated and the fetus is not in any danger, then the cerclage can be placed and the mother closely monitored for the rest of her pregnancy. The success rate for cerclage is quite good, especially if done early in the pregnancy. Roughly 80-90% of pregnant women with incompetent cervices will deliver healthy babies.

The decision to put a woman with an incompetent cervix on prescribed bed rest is controversial and the decision is typically made on a case by case basis. Because some women experience significant contractions in addition to the incompetent cervix, bed rest is used in conjunction with the cerclage and medication to stop the contractions and to prolong pregnancy. For other women, the need for bed rest is not so clear. Many obstetricians fearing pregnancy loss will put women with an incompetent cervix, even if they have a cerclage, on bed rest. Medical Research does not support that this is always necessary.

A test has been developed that is able to predict whether or not a woman is going into preterm labor within the subsequent 2weeks. The fetal fibronectin test checks for the presence of fetal fibronectin, a pregnancy protein found in the cervical plug, in the vagina. If fetal fibronectin is found in the vagina, it means that the cervical plug has somehow been disturbed and a woman may in fact be at risk for preterm labor. If no fetal fibronectin is found, there is a 99% or greater chance that the pregnancy is proceeding and there is no current risk for preterm labor.

The fetal fibronectin test has significant indications for high risk obstetrics. Women at risk of preterm labor may now be tested using the fetal fibronectin test and may avoid prescribed bed rest. Some women may in fact still need to be on modified bed rest, but with the fetal fibronectin test, the current number of 700,000 American women who are prescribed bed rest annually may be reduced.

In my next post I’ll look more closely at the fetal fibronectin test.

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