The cervix is typically around 3–5 centimeters long and gradually shortens during pregnancy. However, sometimes the cervix is shorter than average, which may cause issues during pregnancy.
What does a “short cervix” mean?
The cervix has an internal and an external opening (also called the internal os and external os). The internal os opens into the uterus, and the external os opens into the vagina. During pregnancy, the cervical ossa close to keep the fetus in the uterus and then open when it’s time for delivery.
Over the course of a pregnancy, the cervix shortens and becomes softer to make delivery possible. Some people naturally have a shorter cervix. As their cervix shortens throughout their pregnancy, it may become too short too soon, which increases the risk of preterm labor and premature birth. A short cervix is less than 25 millimeters in length at 18–24 weeks’ gestation. Health care providers measure the length of the cervix with an ultrasound scan.
What causes a short cervix?
The main cause for a short cervix during pregnancy is an insufficient or incompetent cervix. During pregnancy, the baby grows and becomes heavier, pressing on the cervix. If the cervix is short, the pressure from the baby may cause it to open before the baby is ready to be born. This condition is known as an insufficient or incompetent cervix.
Most pregnancy losses in the first trimester are due to chromosomal abnormalities, but an incompetent cervix is the cause of many losses during the second trimester. Insufficient cervix is not very common, however. Only one in 100 pregnancies might result in an incompetent cervix.
In addition to a short cervix, one or more of the following conditions might lead to an insufficient cervix:
- An earlier cervix surgery
- Cervical trauma
- Malformed cervix as a result of a birth defect
- Trauma to the cervix from a miscarriage or abortion
- Diethylstilbestrol (a synthetic estrogen) exposure in utero
- Curettage (removing tissue from the inner lining of the uterus)
- Loop electrocautery excision procedure, used to treat cervical dysplasia
- Uterine anomalies or cervical lacerations with vaginal delivery
Short cervix symptoms
Although often asymptomatic, some mild short cervix symptoms are possible. The symptoms usually appear between 14 and 20 weeks of pregnancy and include:
- Pelvic pressure
- Abdominal cramps
- Change in volume, color, and consistency of vaginal discharge
- Light vaginal spotting or bleeding
- Contractions similar to Braxton-Hicks
Short cervix: possible complications
When the cervix is short, the risk of premature labor and pregnancy loss rises. This is because the cervix might not stay closed for as long as it’s supposed to during pregnancy. Those with a short cervix during pregnancy are more likely to have preterm labor than those with a longer and thicker cervix.
There is treatment for a short cervix. Health care providers may recommend a few different methods to help avoid premature birth. Regular prenatal care makes it possible for a health care provider to discover and treat issues associated with a short cervix in a timely manner.
Short cervix diagnosis
A short cervix can only be detected during pregnancy. A short cervix can’t be diagnosed by a manual exam, but a physical exam can help the health care provider see if the amniotic sac has begun to protrude through the opening (prolapsed fetal membranes). A transvaginal ultrasound is the most reliable way to diagnose a short cervix.
During an ultrasound, a health care provider will measure the cervical length. In a typical pregnancy, the cervix is usually between 3–5 centimeters long (30 to 50 millimeters). The risk of premature birth is greatest when the cervix is less than 2.5 centimeters long. Early detection of a short cervix during pregnancy can help prevent preterm birth and begin treatment before it causes any complications.
How to manage a short cervix
The risk of premature birth and pregnancy loss due to a short cervix can be concerning.
There are ways to manage the risk of a short cervix and prolong the pregnancy. Treatment for a short cervix includes:
- Progesterone: Progesterone is a hormone that is used to prevent contractions and support a pregnancy until it reaches full term. It’s possible to receive the hormone as a weekly injection, as a daily vaginal medication, or vaginal progesterone pessaries until around 34 to 36 weeks. A health care provider may prescribe it in the second trimester or earlier.
- Arabin pessary: The Arabin pessary is another way to reduce the chances of premature pregnancy. It’s a silicone ring that is inserted into the vagina to hold the cervix closed. This is not a surgical procedure, and the placement of the ring is done by an obstetrician. The Arabin pessary placement can increase the risk of an infection.
- Cervical stitch/cerclage: During a cervical cerclage, a stitch is placed in the cervix to help it to stay closed. Cerclage is associated with an 85 to 90 percent successful pregnancy rate. The cerclage is maintained until 36 to 38 weeks of pregnancy or until labor. This procedure is offered to those who have had one or more premature deliveries, late miscarriages, or cervical surgery in the past, and an ultrasound shows that the cervix is opening.
If the diagnosis of a short cervix is made, betamethasone may be used between 24 and 34 weeks of gestation to improve newborn outcomes. Strict bed rest may be recommended as a precautionary measure.
Health care providers will generally also suggest regular monitoring and a consultation with a physician who specializes in high-risk pregnancies. In this way, any issues with a short cervix during pregnancy can be found and treated early.