Cervical Insufficiency

How the cervix normally works

During pregnancy, the cervix stays long, firm and closed, holding the pregnancy inside the uterus. It normally softens, shortens and opens (dilates) only near the end of pregnancy, in response to contractions. In cervical insufficiency, the cervix cannot withstand the growing weight of the pregnancy and opens early, often without any noticeable contractions.

Signs and symptoms

Cervical insufficiency is often silent. When symptoms happen, they are usually mild and appear between about 14 and 24 weeks:

• a sensation of pelvic pressure or heaviness
• a new backache
• mild abdominal cramps
• a change in vaginal discharge: more watery, mucus-like, or tinged with blood
• light spotting or bleeding

If not detected, the cervix may open enough that the amniotic sac bulges into the vagina, the waters break, or the pregnancy is lost.

Causes and risk factors

• Previous painless second-trimester loss or early preterm birth: the strongest risk factor
• Cervical surgery: cone biopsy or LEEP for abnormal Pap smears
• Repeated or forceful cervical dilation during D&C procedures
• Cervical tears in a previous delivery
• Uterine or cervical abnormalities present from birth
• Connective tissue disorders such as Ehlers-Danlos syndrome
• Prenatal exposure to DES (rare now)

Many people have no known risk factor.

Diagnosis

There is no single test. Diagnosis is based on:

1. Obstetric history: one or more painless second-trimester losses without labor or bleeding.
2. Transvaginal ultrasound: measures cervical length. A cervical length of less than 25 mm (1 inch) before 24 weeks is considered short and raises the risk of preterm birth.
3. Physical examination: a speculum or digital exam may show a painlessly dilated cervix in the second trimester.

Many practices offer cervical length screening during the routine anatomy scan at 18 to 22 weeks.

Treatment

Cervical cerclage

A cerclage is a strong stitch placed around the cervix to help keep it closed. Types:

• History-indicated cerclage: placed at 12 to 14 weeks in people with a history of second-trimester losses caused by cervical insufficiency.
• Ultrasound-indicated cerclage: for people with a prior preterm birth who develop a cervix shorter than 25 mm before 24 weeks.
• Physical exam-indicated (rescue) cerclage: when the cervix is already dilated in the second trimester, without labor or infection.
• Transabdominal cerclage: placed through the abdomen, before or early in pregnancy, when vaginal cerclage has failed.

The stitch is usually removed at about 36 to 37 weeks, or earlier if labor starts. Risks include infection, bleeding and rupture of membranes.

Vaginal progesterone

Daily vaginal progesterone reduces the risk of preterm birth in people with a short cervix found on ultrasound, particularly without a previous preterm birth.

Other measures

• serial ultrasound monitoring of cervical length
• treating infections
• strict bed rest and activity restriction are not recommended, because they have not been shown to help and carry risks such as blood clots
• if preterm birth is likely, steroid injections help the baby's lungs, and magnesium sulfate protects the baby's brain before 32 weeks

Complications

• miscarriage in the second trimester
• preterm birth with risks to the baby from prematurity
• premature rupture of the membranes
• infection of the membranes (chorioamnionitis)

Future pregnancies

After a loss due to cervical insufficiency, the risk of recurrence is significant, but with early monitoring, cerclage or progesterone, many people go on to have term or near-term births. A preconception visit with an obstetrician or maternal-fetal medicine specialist allows a plan to be made before pregnancy.

Frequently asked questions

What are the signs of an incompetent cervix?

Many people have no symptoms. Possible signs between 14 and 24 weeks include pelvic pressure, a new backache, mild cramps, and a change in vaginal discharge or spotting. Any of these in the second trimester should be checked promptly.

Can cervical insufficiency be prevented?

It cannot always be prevented, but early detection with ultrasound and treatment with a cerclage or vaginal progesterone greatly lowers the risk of loss or very early birth in high-risk pregnancies.

What is a short cervix in pregnancy?

A short cervix is one measuring less than 25 mm (about 1 inch) on transvaginal ultrasound before 24 weeks. It raises the risk of preterm birth and may be treated with progesterone or, in some cases, cerclage.

Is bed rest needed for cervical insufficiency?

No. Studies have not shown that bed rest prevents preterm birth, and it increases the risk of blood clots and muscle loss. Your doctor may advise avoiding heavy lifting or intercourse in some cases.