What exactly is the cervix?

The cervix is the narrow, tubular, lower end of the uterus that extends into the vagina. (The word cervix means "neck" in Latin.) When you're not pregnant, the cervical canal remains open a tiny bit to allow sperm to enter the uterus and menstrual blood to flow out. 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. At that point it usually starts to soften, efface (grow shorter), and dilate (open up) as your body prepares for labor.

What does it mean to have cervical insufficiency?

If your cervix is softer and weaker than normal or is abnormally short to begin with, it may efface and dilate without contractions in the second or early third trimester as the weight of your growing baby puts increasing pressure on it. This condition — known as cervical insufficiency (sometimes called "incompetent cervix") — can result in second-trimester miscarriage; preterm premature rupture of the membranes (PPROM), in which your water breaks before you're full-term and before you're in labor; or preterm delivery (before 37 weeks). It particularly increases your risk for early preterm delivery, which means giving birth before 32 weeks.

How would I know if I had cervical insufficiency?

In the past, you would have been diagnosed with cervical insufficiency after you had had several second-trimester miscarriages or early preterm births from no other known cause. Now if you're at risk for this condition, your practitioner may order regular transvaginal ultrasounds beginning at 16 to 20 weeks to measure the length of your cervix and to check for signs of early effacement (shortening).

If she finds significant changes, you're at a much higher risk for preterm birth. And the shorter your cervix, the greater the risk. But diagnosing this condition is still tricky, and there's a lot of controversy about whether any treatment strategies will help prevent a late miscarriage or preterm delivery. One benefit of having early warning that your cervix is changing is that it gives you time to take corticosteroids, which help minimize health problems in premature babies. Call your practitioner immediately if you have any of these symptoms:

• Change in amount or type of vaginal discharge, particularly a mucousy or watery discharge
• Vaginal spotting or bleeding
• Menstrual-like cramping
• Pelvic pressure or "heaviness"

Who's most at risk for cervical insufficiency?

You're more likely to have this condition if:

• You've had a second-trimester miscarriage with no known cause or an early spontaneous preterm delivery in a previous pregnancy that wasn't caused by preterm labor or a placental abruption. It's even more likely if you've had more than one late miscarriage or early spontaneous preterm birth.
• You've had a procedure such as a cone biopsy or LEEP done on your cervix.
• Your mother took the drug DES while she was pregnant with you. (Caregivers used to prescribe this drug to prevent miscarriage, but stopped in the early 1970s when studies showed that it was both ineffective and caused reproductive tract abnormalities in developing babies.)
• Your cervix was injured during a previous birth or dilation and curettage (D&C), or you've had several pregnancies terminated.
• You have an unusually short cervix.

Is there anything I can do about it?

If ultrasound shows you have an abnormally short cervix and you're less than 24 weeks pregnant, your practitioner may recommend a cerclage, a procedure in which she stitches a band of strong thread around your cervix to reinforce it and help hold it closed. However, there's a lot of controversy about whether cerclage should be used in this situation.

Some recent research questions the effectiveness of the procedure at preventing miscarriage, PPROM, or preterm birth except in a small number of circumstances. And the procedure itself can cause problems that lead to preterm delivery, including uterine infection, ruptured membranes, and uterine "irritation" leading to contractions.

Experts are trying to figure out whether, in certain situations, the benefits of cerclage outweigh the risks. Women who seem to benefit from cerclage include those who've had three or more unexplained second-trimester losses or preterm births. If you're in this group, you're likely to get a cerclage at 13 to 16 weeks, before your cervix starts to change. A cerclage done then appears less risky than one done later in pregnancy, after your cervix has started to change.

Cerclage is performed using a general, spinal, or epidural anesthetic. If you have one, you'll be able to go home that day or the next. You'll be told to relax for a few days, during which you may have light bleeding or cramping. You'll need to stop having sex for a while (or possibly for the rest of your pregnancy). Your practitioner may give you medication to prevent infection or preterm labor, and she'll continue to check your cervix regularly for signs of further changes until the stitches come out, usually at 37 weeks. Once you reach that point, you can relax and wait for labor to begin.

Some caregivers prescribe bedrest in addition to — or instead of — cerclage. Although there's no solid evidence that staying in bed is effective, the theory is that keeping the weight of the uterus off of a weakened cervix might help. You'll probably be told to abstain from sex as well.