Cervical length is the length of the cervix. The cervix is the lower end of the uterus. The cervix holds the unborn baby, called a fetus, in the uterus until birth.

During pregnancy, the length of the cervix might shorten too early. That raises the risk of going into labor early, called preterm labor, and giving birth too soon, called preterm birth. Preterm labor happens after week 20 and before week 37 of pregnancy. The earlier a preterm birth happens, the greater the health risks for the baby.

The cervix is the lower part of the uterus that connects to the vagina. Before pregnancy, the cervix is closed, long and firm. During pregnancy, the cervix gradually softens. Just before labor, the cervix gets shorter. In the final stage of pregnancy, the cervix opens as the body gets ready to give birth. If the cervix begins to open before 37 weeks of pregnancy, premature birth could happen.

The cervix typically gets shorter without causing any noticeable symptoms. Often a cervix that shortens early can be seen during a routine ultrasound.

Sometimes, symptoms of preterm labor may happen when the cervix gets shorter. Preterm labor symptoms may include:

• Contractions that happen often and consistently.
• A low, dull backache that doesn't go away.
• Cramps.
• A change in discharge that comes out of the vagina.
• A feeling of pressure in the pelvis.

If you have symptoms of preterm labor, your healthcare professional might do an ultrasound through the vagina to check the length of the cervix. If the cervix is less than 29 millimeters but greater than 25 millimeters, more ultrasounds may be needed to monitor the cervix as pregnancy goes on.

If the cervix is less than 25 millimeters before 24 weeks of pregnancy, a procedure called cervical cerclage may help prevent preterm birth. This procedure uses stitches or tape to keep the cervix closed. The stitches or tape are taken out later in pregnancy. Cervical cerclage typically is not used for people who are pregnant with twins or other multiples. It may be helpful earlier in pregnancy for some people who have had a preterm birth before.

Treatment with the hormone progesterone may help lower the risk of premature birth for people whose cervix has shortened early. Progesterone may be recommended for those who:

• Have a cervix length of 25 millimeters or less.
• Haven't reached 25 weeks of pregnancy.
• Do not have symptoms of preterm labor.
• Are not pregnant with twins or other multiples.
• Have not given birth before 37 weeks in an earlier pregnancy.

Bed rest and limits on other activity used to be advised for people at high risk of preterm birth. But there's no evidence to show that activity restrictions help keep a baby from being born too soon. Most healthcare professionals no longer recommend them.

If you're worried about cervical length during pregnancy, talk with your healthcare professional. If you have any symptoms of preterm labor, contact a member of your healthcare team right away.