Cervical insufficiency, sometimes called incompetent cervix, affects roughly 1% of pregnancies. In a 2012 study of over 34,000 pregnant women, about 401 received the diagnosis. While that makes it relatively uncommon, it remains one of the leading causes of pregnancy loss and extremely preterm delivery in the second trimester, which is why it gets outsized attention from maternal health specialists.
When It Typically Happens
In a healthy pregnancy, the cervix stays firm and closed until labor begins. With cervical insufficiency, the cervix softens, shortens, and opens too early, often without any contractions or pain. This usually happens between weeks 16 and 24 of pregnancy, with the highest risk window falling between weeks 18 and 22. Because it’s painless, many women don’t realize anything is wrong until significant dilation has already occurred or membranes have ruptured.
How It’s Diagnosed
The primary tool is transvaginal ultrasound, which measures cervical length. Before 24 weeks, a cervix measuring 25 millimeters or shorter is considered short and raises concern. At that gestational age, 25 mm falls around the 2nd to 3rd percentile, meaning the vast majority of pregnant women have a longer cervix at the same point in pregnancy.
For women with no prior preterm births, a short cervix found on routine ultrasound triggers closer monitoring. For those with a history of second-trimester loss or very early preterm delivery, providers often begin cervical length screening around 16 weeks and repeat it every one to two weeks through 24 weeks to catch changes early.
What Raises Your Risk
The most significant risk factor is a prior second-trimester loss or early preterm birth caused by cervical insufficiency. Without treatment, there’s about a 30% chance it will happen again in a subsequent pregnancy.
Prior cervical procedures also play a role, though the picture is more nuanced than many women expect. Cone biopsy, an older and more extensive cervical surgery, has long been linked to higher miscarriage rates. The data on LEEP (a more common procedure used to treat abnormal cervical cells) is more reassuring. Studies show no significant increase in miscarriage risk if at least 12 months pass between a LEEP and conception. However, when pregnancy occurs within 12 months of LEEP, the miscarriage rate roughly doubles compared to women who never had the procedure (28.2% versus 13.4%).
Other risk factors include carrying twins or higher-order multiples, having a connective tissue disorder like Ehlers-Danlos syndrome, uterine abnormalities, and a history of cervical trauma during a prior delivery.
Treatment Options and How Well They Work
Three main approaches are used to prevent preterm birth in women with a short cervix: cerclage (a stitch placed around the cervix to hold it closed), a cervical pessary (a silicone device placed around the cervix for support), and vaginal progesterone (a hormone that helps maintain the cervix). A large randomized trial comparing all three found no significant difference in preterm birth rates before 37 weeks: 29.9% for cerclage, 31.1% for the pessary, and 24.2% for progesterone. The choice often comes down to the clinical scenario, patient history, and provider experience.
When cervical insufficiency is diagnosed as an emergency, meaning the cervix is already significantly dilated, the stakes are higher but treatment still helps. Emergency cerclage reduces the rate of delivery before 28 weeks by about 55% compared to bed rest alone. Overall fetal survival after emergency cerclage is around 88%, with neonatal survival at 90%.
Transabdominal Cerclage for Recurrent Cases
For women who have had a prior cerclage fail or whose cervix is too short or damaged for a standard vaginal stitch, a transabdominal cerclage is a more involved surgical option. The stitch is placed higher up, closer to where the cervix meets the uterus, either through a small abdominal incision or laparoscopically. It can be placed before or during pregnancy. Success rates are high: 95% to 98% of patients deliver at 36 weeks or later. Because the stitch is permanent, delivery requires a cesarean section.
What 1% Actually Means for You
A 1% prevalence can feel both reassuring and misleading. If you’ve never had a second-trimester loss or early preterm birth, your individual risk is likely lower than 1%. If you have one or more risk factors, particularly a prior loss between 16 and 24 weeks, your risk is substantially higher. The 30% recurrence rate without treatment underscores why women with a history of cervical insufficiency are monitored closely in every subsequent pregnancy.
The good news is that once identified, cervical insufficiency is one of the more treatable causes of pregnancy loss. Whether through progesterone, cerclage, or a combination, the majority of women with the diagnosis go on to deliver viable, healthy babies. Early and consistent cervical length monitoring is the single most important step for anyone at elevated risk.