Pinky Ronen, M.D.
The cervix is the opening of the uterus. In the normal state it is a tubular structure that measures more than 3 centimeters and protrudes into the vagina. During a normal pregnancy, the cervix remains firm, long, and closed until late in the third trimester. At that point it usually starts to soften, efface (grow shorter), and dilate (open up) as your body prepares for labor.
Incompetent cervical os (also called “Cervical Insufficiency”) is a condition in which the cervix opens and shortens prematurely. This usually happens between 16 and 20 weeks of gestation, though it can happen later in pregnancy at times. The opening of the cervix is “silent” in that there is no associated pain or other symptoms. As the cervix opens the pregnancy sac gradually drops beyond the cervix into the vagina resulting in premature rupture of the amniotic sac and delivery of the fetus. When this happens before 22-24 weeks the fetuses almost always die because they are too premature to sustain life.
Incompetent Cervix is usually diagnosed late because there are no associated symptoms or warning signs until late in the process. Occasionally it is diagnosed early in the pregnancy and an emergency cerclage (stitching of the cervix) can be performed in an attempt to close the cervix and prolong the pregnancy. Usually the diagnosis is late and a cerclage is not possible. In these cases some prolongation of the pregnancy can be achieved by resting the patient in bed at an inclined position with the head low and the legs high, thereby relieving pressure and gravitational forces from the pregnancy. This treatment mode poses a dilemma when there is premature rupture of the amniotic sac at the very early gestational age. When this happens a severe infection of the pregnancy and uterus is imminent and the fetus almost never survives. The mother is at great risk for severe complications and even death from the infection. Some doctors advocate actively delivering the very premature fetus to avoid such an infection. This is always a very difficult decision and can be done only with the consent of the parents.
Most of the times Incompetent Cervix occurs without any risk factors. In some patients there are risk factors for an Incompetent cervix.
Risk factors for incompetent cervical os include:
- A previous pregnancy with incompetent os
- A patient who has had surgeries or procedures done on the cervix
- A patient who was expose to DES while she was a fetus herself
- A patient with a congenital anomaly of the cervix or uterus
- A patient who had trauma at birth or other to the cervix
Patients with risk factors should be monitored very closely during pregnancy. If there are significant risk factors or there is evidence that the cervix is shortening as pregnancy progress, most doctors would recommend a preventative placement of a cerclage. This is usually done in the early second trimester (around 13 weeks).