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    What Having a Short Cervix During Pregnancy Means

    Updated 23 February 2021 |
    Published 05 March 2019
    Fact Checked
    Natalia Viarenich, MD
    Reviewed by Natalia Viarenich, MD, Obstetrician-Gynecologist, Lithuania
    Flo Fact-Checking Standards

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    The cervix is the cylindrical part of the uterus that connects the uterus to the vagina. Before pregnancy, the cervix is closed, long, and firm. Its main role is to secrete fluids that help sperm travel from the vaginal canal to the uterus. 

    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: 

    A doctor explains to a woman what a short cervix during pregnancy means

    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.

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