Having a short cervix can complicate labor and delivery. If a doctor recognizes this potential issue early on, it can make treatment easier and more effective.
If a pregnant woman’s cervix is short, it may lead to cervical insufficiency.
Cervical insufficiency refers to the cervix dilating too soon. This can increase the risk of pregnancy loss, preterm labor and delivery, and other complications.
When the cervix is unusually short, it is prone to dilation, and it provides less protection for the fetus and pregnant woman.
Having a short cervix increases the risk of pregnancy loss, preterm labor, and early delivery.
Doctors define preterm labor as cervical changes that happen before 37 weeks of pregnancy.
Preterm labor is a risk factor for numerous complications, including stillbirth, low birth weight, bleeding in the brain, and long-term disabilities.
Drawing on previous research, the Society for Maternal-Fetal Medicine report that a short cervix increases the risk of preterm labor six-fold in women pregnant with one fetus and eight-fold in women pregnant with twins.
While many factors can cause preterm birth, researchers consistently find a clear correlation between having a short cervix and going into premature labor.
For example, one study of women with very short cervixes — of less than 15 millimeters (mm) — found that this issue accounted for 86% of cases of preterm labor before 28 weeks and 58% of cases of preterm labor before 32 weeks.
While doctors often measure the length of the cervix during early pregnancy ultrasounds, a transvaginal ultrasound gives the most reliable measurement. This type of ultrasound involves inserting the transducer into the vagina to get a clearer image of the cervix.
A 2017 study found that when a transabdominal ultrasound indicated that the cervix was shorter than 29 mm, a vaginal ultrasound was likely to confirm that the cervix was clinically short.
The Society for Maternal-Fetal Medicine recommend routine cervical length screening for pregnant women with a history of preterm labor or delivery.
If a clinician thinks that a woman may have a short cervix, they may begin checking the length via transvaginal ultrasound between weeks 16 and 20. If a woman has a history of preterm labor or short cervix diagnosis, they may begin the checks even earlier.
If the cervix is less than 25 mm long (about 1 inch), doctors generally consider it to be short. However, some doctors use different standards, and they may consider a length of 20–30 mm to be short.
Overall, it is important for anyone with a history of preterm labor or a short cervix to let their doctor know.
There are generally two treatment options for a short cervix.
For some women, a doctor may recommend a cerclage. This is a stitch in the cervix that reinforces it, reducing the risk of pregnancy loss or preterm labor.
Doctors advise against cerclage for women with twin or other multiple pregnancies.
A cerclage works best when a doctor performs it in early pregnancy. Most doctors will not carry out the procedure after 23 weeks.
A 2017 review of 15 studies concluded that — while cerclage reduces the risk of preterm birth in women at high risk — it is still unclear whether other options may be more effective, particularly vaginal progesterone.
Vaginal progesterone can be administered with suppositories or injections. A doctor may, for example, recommend suppositories for a woman who has a short cervix but no history of preterm delivery.
According to a 2013 study, vaginal progesterone reduces the risk of delivering before 33 weeks by 44%.
It may not be possible to tell why the cervix is shorter than average.
Some risk factors for a short cervix and cervical insufficiency include:
- malformations of the uterus, such as having a uterus that is split into two sections
- past surgery on the cervix
- injuries to the uterus or cervix during a previous delivery
- inflammation or infection of the cervix or vagina
- pregnancies that are very close together
Women who have experienced previous premature delivery have a higher risk of future premature deliveries.
Most women do not know the length of their cervixes. It may be a good idea for women with a history of preterm labor, cervical injury, or late pregnancy loss to have the length checked.
Every pregnant woman should speak with a doctor about their individual risk factors.
Anyone who feels anxious about the potential for preterm delivery can request a transvaginal cervical measurement, even if they have no risk factors.
Pregnant women with short cervixes should seek medical attention if:
- They have bleeding from the vagina.
- They have symptoms of labor, such as contractions.
- They notice fluid leaking from the vagina.
- The fetus stops moving or moves less frequently.
If it is not possible to get in touch with the doctor or see them that day, visit an emergency room.
Treatment for a short cervix is most effective if it begins before 24 weeks of pregnancy.
Pregnant women who receive this treatment often have uncomplicated pregnancies and delivery.
Even when a woman goes into premature labor, progesterone or cerclage may still delay labor by several weeks, giving the fetus more time to develop. This decreases the risk of complications.