Short Cervix in Pregnancy
What is A Short Cervix?
The cervix is the narrow, lower end of the uterus that opens into
the vagina. The cervix has a firm texture, similar to the tip of
your nose, and is normally about 35 to 48 mm (1.4 to 1.9 inches)
long at 24 weeks. The cervix is considered to be short if the length of the
cervix is less than 25 mm long before 24 weeks of gestation. The
chances for having a preterm birth are higher in women who have a short
During pregnancy the cervix remains closed and firm
acting as a barrier to infection and supporting the weight of your growing
baby. At around 32 weeks' your cervix naturally begins to soften, shorten,
and become thinner until it is eventually paper thin and almost vanishes
This process of shortening and thinning is called effacement and is
measured by your doctor or nurse during a vaginal examination. Effacement is
reported as a percentage from zero percent (normal length cervix) to 100% or
complete (paper thin cervix).
How the Cervix is Measured Using Ultrasound
effacement begins at the internal opening of the cervix, effacement can
usually be detected at an earlier stage by ultrasound examination.
The cervical length (CL) is
usually measured when the bladder is empty using a transvaginal
ultrasound (TVU) probe. The length of your cervix is measured from its internal opening
on the inside of the uterus to its external opening into the vagina.
ultrasound is used to measure the length of the cervix, the length of
the cervix is reported in millimeters (mm) or centimeters (cm) instead
of as a percentage.
Normally the cervix is about 35
to 48 mm (1.4 to 1.9 inches) long at 24 weeks.
Image The National Institutes of Health
The cervix is considered to be short if the length of the
cervix is less than 25 mm long before 24
weeks of gestation.
The cervix is considered to be very short if the length of
the cervix is less than or equal to 20 mm at up to 24
weeks of gestation
Short Cervix and Preterm Birth
Having a short cervix increases the chances that you will
have a preterm delivery. As the graph below shows, the chances of having a preterm delivery increase
as the length of the cervix becomes shorter.
A short cervix is not the same as cervical insufficiency.
Cervical insufficiency (sometimes called an incompetent cervix) is the failure
of the cervix to maintain a pregnancy when there are no signs or symptoms
of labor in the second trimester. A short
cervix by itself is not sufficient for the diagnosis of cervical
Women who have had biopsy, loop electrosurgical excision procedures (LEEP)
, dilation and curettage (D&C), uterine malformations or exposure to
diethylstilbestrol may be at increased risk for cervical insufficiency.
Cervical insufficiency can sometimes be treated using cervical cerclage. A
cerclage is a stitch placed, under anesthesia, around the cervix to keep it
closed. ACOG recommends that cerclage should be limited to pregnancies in the
second trimester before fetal viability has been achieved. Activity restriction,
bed rest, and pelvic rest have not been shown to be effective treatments for cervical
The American College of Obstetricians and Gynecologists (ACOG) recommends:
Treatment for the Prevention of Preterm Labor
- In women with a singleton pregnancy , no history for preterm birth
, and cervical length is 20 mm or less before or at 24 weeks
Vaginal progesterone 8% gel (90 mg daily) OR
Micronized progesterone capsules (200 mg vaginally daily)
- Progesterone is a substance produced by the ovary and placenta that
acts to prepare for and maintain pregnancy . Progesterone has been shown
to help prevent the cervix from shortening in some women.
Placement of cerclage in women with a cervical length less than 25 mm between
16 weeks and 24 weeks
and no history of preterm birth has not been associated with a significant
reduction in preterm birth 
- In women with a singleton pregnancy, with a history of preterm birth at less than 34 weeks, already receiving progesterone
since 16 weeks cerclage should be considered if the cervical length
is less than 25 mm before 24 weeks.
- A cerclage is a stitch placed around the cervix to keep it closed.
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Lippincott Williams & Wilkins. All rights reserved
- In women with a twin or triplet pregnancy neither progesterone treatment
or cerclage reduce the rate of preterm birth. Neither is recommended to prevent
preterm birth in these groups of women.
- Some groups are studying the use of a cerclage pessary, a small ring-shaped
device which is inserted around the cervix, to prevent preterm births in twin
An analysis by the Perinatology Research Branch of the
National Institute of Child Health and Human Development found that
vaginal progesterone or cerclage are probably equally effective in the
prevention of preterm birth in women with a singleton pregnancy , with a history
of preterm birth, and who are found to have a short cervix in the second
trimester. The choice of treatment needs to consider adverse events, cost and
Treatment of Preterm Labor
If your are having symptoms such as cramping, your cervix is
shortening very quickly, or your cervix is less than 15 mm, your doctor or
admit you to the hospital for additional evaluation or treatment . Besides a short cervix, preterm labor may also be caused by infection,
inflammation, vascular disease (poor blood supply to the uterus and placenta) ,
an overstretched uterus, and abnormalities of the cervix . The cause of many
preterm births is never found.
Your provider may collect a sample of fluid from your vagina to test for a substance called fetal fibronectin (fFN) . Fetal fibronectin (fFN) acts like "glue" holding the fetal sac to the uterine lining during pregnancy. The
presence of fetal fibronectin in the vagina between 24 and 34 weeks of
pregnancy makes it more likely that you will have a preterm delivery.
If there is enough time you can be given a medication (corticosteroid) to
help your baby's lungs mature and reduce other complications of being born prematurely.
Medications such as nifedipine , terbutaline,
or indocin may be given for up to 48 hours to help control your contractions.
You may also be given intravenous magnesium to lessen the chances of your baby having cerebral palsy due
to being born prematurely .
Once preterm labor has been stopped bedrest and long term use of medications such as nifedipine , terbutaline,
indocin, or magnesium to stop contractions are not recommended because these treatments are either ineffective
and/or may cause harm . The use of progesterone to prolong pregnancy once
preterm labor has been stopped is being studied.
and Low Lying Placenta or Placenta Previa
Women who have placenta previa and a cervical length of less than or equal to 30 mm are more likely to have
emergency Cesarean section and experience larger
blood loss before and during surgery.
Reviewed by Mark Curran, M.D. FACOG
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