What is an Incompetent Cervix?

When a pregnant woman goes into labor her cervix begins to dilate, making way for the baby to pass through. Normally the cervix remains closed until labor, holding the fetus and amniotic sac in place. In the case of an incompetent cervix, however - also known as a weak cervix or cervical insufficiency - pressure placed on the cervix by the growing baby causes the cervix to dilate prematurely. The membranes (or walls) of the amniotic sac holding the fetus gradually stretch, weaken, and eventually break, resulting in a spontaneous loss of the baby or a premature delivery..

Unlike a miscarriage that is common during the first three months of pregnancy, an incompetent cervix usually occurs during the second trimester, when the loss of a baby is more likely to be caused by underlying medical problem. While not a common complication of pregnancy, an estimated 20-25% (1 out of 100) of all second-trimester losses are said to be brought on by a weak or incompetent cervix.


An incompetent cervix can be caused by:

· Previous cervical surgeries or biopsies

· Previous damage from a difficult birth

· Previous cervical trauma, i.e., a D&C (dilation and curettage) or miscarriage

· Malformed cervix or uterus resulting from a birth defect

· Fetal exposure of the mother to Diethylstilbestrol (DES)

· Repeated late-term abortions


Since there are often no warning signs of an incompetent cervix, the condition is usually not diagnosed until after a second or third trimester miscarriage has occurred. Therefore, pregnant women are not routinely checked for cervical incompetence unless they have one of the above risk factors. However, if a pregnant woman has experienced previous losses in the second or third trimester, it is generally assumed that she has or is at risk for a weakened cervix.

Diagnosis can be made simply by a manual pelvic exam or by an ultrasound. A pelvic exam determines whether the cervix is dilating. An ultrasound measures the cervical opening and the length of the cervix.


The good news is that if cervical incompetence is detected early, it is possible to prevent the loss of the baby. In a procedure called cerclage, the cervix is stitched closed to reinforce the weak cervix while the baby develops. Cerclage is usually performed between weeks 14 and 16 of pregnancy, under a local or general anesthetic, and the stitches are removed around weeks 36 to 38 to allow for a vaginal birth process to occur. Medications are sometimes prescribed in conjunction with cerclage.

Although once weakened a cervix cannot be strengthened, these treatment measures have a high success rate of 85-90%, where the use of cerclage and drug therapy result in women carrying to term and the birth of healthy babies.


Rare but possible complications associated with cervical cerclage include:

Cervical laceration; rupture of the uterus or bladder; maternal hemorrhage; preterm labor; premature rupture of the membranes.


Women with the following conditions are not candidates to have a cervical cerclage:

· Cervix is dilated 4cm or more

· Cervix is irritated

· The amniotic membranes have ruptured and water has broken

· The fetus has already died

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