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Home > Wellness > Health Library > Preterm Labor and Short Cervix
During pregnancy, the
cervix is a closed and sealed tunnel between the
uterus and the vagina. Before or during labor and delivery, the cervix
stretches and flattens (effacement). At 24 weeks of pregnancy, the average
cervix is about 35 mm (1.4 in.) long.1
ultrasound imaging, researchers have found that at the
end of the second trimester (about 24 weeks), the shorter a woman's cervical
length, the more likely she is to deliver preterm. (This type of cervical
measurement requires special training and experience to perform accurately.)
Cervical length of less than
25 mm (1 in.) before 35 weeks
is considered a reliable sign of increased preterm labor risk. However, most
women with a shortened cervix do go on to deliver at term.2
If you have preexisting risk factors for preterm labor, the
absence of a shortened cervix is a reassuring sign that
preterm labor is not imminent.
There is a lack of proven treatment options for preventing preterm
labor over a period of weeks. So, knowing that you have a shortened cervix and
increased preterm labor risk may not change the way your doctor treats your
pregnancy.2 If you learn that you are at high risk,
make sure that you know the symptoms of preterm labor and that you know what to
do if you have them.
Cunningham FG, et al., eds. (2010). Preterm birth. In
Williams Obstetrics, 23rd ed., pp. 804–831. New York:
American College of Obstetricians and Gynecologists
(2001, reaffirmed 2010). Assessment of risk factors for preterm birth. ACOG
Practice Bulletin No. 31. Obstetrics and Gynecology,
January 10, 2011
Sarah Marshall, MD - Family Medicine & William Gilbert, MD - Maternal and Fetal Medicine
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