As your pregnancy progresses and your baby grows larger and heavier, an increasing amount of pressure is placed on your cervix. In some women, this may cause their cervix to efface and dilate without contractions, a condition called cervical insufficiency or an incompetent cervix that can lead to miscarriage, preterm rupture of the membranes, premature delivery, and early preterm delivery (before 32 weeks). While an incompetent cervix occurs in only 1 out of 100 pregnancies, the condition is responsible for approximately 25 percent of miscarriages in the second trimester.
Your cervix is the narrow, tubular, lower end of the uterus that extends into the vagina. When you're not pregnant, your cervix remains open a tiny bit to allow sperm to enter the uterus and menstrual blood to flow out. However, once you become pregnant, secretions fill the canal and form a protective barrier called the mucous plug. During a normal pregnancy, the cervix remains firm, long, and closed until late in the third trimester when it usually begins to soften, efface (grow shorter), and dilate (open up) as your body prepares for labor. With an incompetent cervix, the amniotic membranes surrounding the fetus bulge down into the opening of the cervix until they break, resulting in the loss of the baby or a very premature delivery.
Generally, there are no symptoms associated with an incompetent cervix and few women realize they have the condition until they miscarry - usually four months into their pregnancy or later. Symptoms of a miscarriage due to an incompetent cervix include abdominal pressure and feeling a "bump" in the vagina. If you have an incompetent cervix with one pregnancy, you will have to take precautions with all subsequent pregnancies.
The causes of an incompetent cervix are not always known; some women are just born with an unusually short or soft cervix. However, you're more likely to have this condition if:
- Your cervix was injured during a previous birth or dilation and curettage (D&C), or you've had several pregnancies terminated.
- You've had a previous miscarriage in the second trimester that had no identifiable cause, or an early spontaneous preterm delivery that was not caused by preterm labor or a placental abruption. Your risk increases if you've had more than one late miscarriage or early spontaneous preterm birth.
- Your mother took the drug DES while she was pregnant with you.
- You've had a cone biopsy or LEEP (Loop Electrosurgical Excision Procedure). These are generally done to treat cervical dysplasia, a precancerous change in the skin on the cervix.
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