About 80% of all pregnancy losses occur in the first trimester, but a small fraction of women will suffer miscarriage or stillbirth in the second or third trimester. The majority of late pregnancy losses are never explained, but researchers have identified some factors that can cause women to suffer recurrent late miscarriages. One of those few recognized causes of late pregnancy losses is a condition called cervical insufficiency, often referred to as "incompetent cervix."
A woman with cervical insufficiency may experience preterm births or late pregnancy losses due to her cervix starting to dilate too early in the pregnancy. The early dilation leads to an early delivery of the baby that can't be stopped by intervention in cases when the problem isn't caught in advance. Often the baby is born too early for it to survive. Unfortunately, catching cervical insufficiency early can be tricky.
If you've had one or more second-trimester miscarriages or preterm births, you may be wondering whether you might have cervical insufficiency. How can you tell if it might be an explanation for your situation? Here is what UpToDate, an online health reference site for doctors and patients, has to say about warning signs in a patient's history that might suggest cervical insufficiency:
"A history of recurrent second trimester pregnancy loss should alert the clinician to the possibility of cervical insufficiency. Other, more subtle, markers of reduced cervical resistance include a soft cervical consistency on digital examination, a history of short labors, advanced dilatation before the onset of labor, and progressively earlier deliveries with each successive pregnancy."
If you've had multiple second-trimester miscarriages or stillbirths, it's worth asking your doctor about whether you might be at risk. If you have delivered quickly in your past pregnancies or if you have been going into labor earlier with each pregnancy, you should share your concerns with your doctor and discuss whether you need monitoring for incompetent cervix in future pregnancies.
But even having these signs only means that cervical insufficiency might be a possibility -- the diagnosis can't be confirmed simply by having risk factors. If your doctor feels you are at risk, she will probably monitor you closely in your next pregnancy for the clear clinical signs of cervical insufficiency.
Here are some further questions you might have:
Can incompetent cervix cause recurrent first-trimester miscarriages?
No, cervical insufficiency wouldn't be a factor in a first-trimester miscarriage. A woman with cervical insufficiency would start to dilate as the baby grew larger and began to place more pressure on the cervix. In the first trimester, the developing baby is too small for this to be an issue. If you are having recurrent first-trimester miscarriages, you should talk to your doctor about being tested for recurrent miscarriage causes. It is not likely that cervical insufficiency will be the explanation in your case, though.
Can I be tested before I get pregnant again?
Unfortunately, there's no reliable test for cervical insufficiency in women who aren't pregnant. In women who are pregnant and who have risk factors for preterm delivery due to cervical insufficiency, doctors can screen for symptoms in the early second trimester via ultrasound and pelvic exam. If your doctor believes you are at high risk for cervical insufficiency, she will probably screen you early in the second trimester of your next pregnancy.
Why aren't all women routinely screened for cervical insufficiency in the second trimester?
Research has shown that screening isn't effective in women without a history of second-trimester miscarriages or preterm birth. Having a short cervix on ultrasound isn't always predictive of preterm birth, and screening women at low-risk could lead to unnecessary interventions.
What's the treatment if my doctor believes I have an incompetent cervix?
Practices vary among physicians, mainly due to the lack of clear evidence indicating a specific course of action. Some doctors will recommend placement of a cervical cerclage (a stitch to help hold the cervix closed) as a precautionary measure early in the pregnancy. Other doctors will recommend close monitoring and place an emergency cerclage if needed. Although some studies show benefits to cerclage in preventing early delivery, there's a lot of conflicting evidence on which women will benefit from it and when in pregnancy it is best to place the cerclage.
Why do some doctors refuse to consider cervical insufficiency until you've had two second-trimester miscarriages?
From a patient's perspective, it can seem almost cruel when a doctor tells you that you have to miscarry again before you can be tested for treatable causes. In a perfect world, it would be possible to screen for everything potentially treatable in anyone who's had one miscarriage -- or even to screen for problems before you even get pregnant once. Unfortunately, we haven't yet reached the point where that's possible. With conditions like cervical insufficiency, the diagnostic criteria are still unclear. What's normal in one person can be signs of problems in another. There are risks -- some serious -- to using intervention in people who don't really need it. Having a history of second-trimester miscarriage makes it more likely that treatment in a future pregnancy would help rather than hurt.
From my research, I think there's a chance my miscarriage may have been caused by cervical insufficiency. But my doctor won't test me for it. What should I do?
That's worth discussing with your doctor. It's OK to ask your doctor for a detailed explanation of why he or she doesn't believe cervical insufficiency is a factor in your situation. It's also OK to seek a second opinion if you don't agree with your doctor's conclusion.
Want to learn more? See UpToDate's topic, "Cervical insufficiency," for additional in-depth medical information.
Johnson, Jeffrey R. and Jay D. Iams. "Cervical insufficiency." UpToDate. Accessed: Dec 2009.