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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5802_Библиотеки_им_академика_М_И_Перельмана.pdf
Obstetrics
396
Length of the cervix and cervical
canal in pregnancy
PREPARATION
Empty bladder.
POSITION
Mother is in the lithotomy position. If the digital exam reveals that the
cervix is already dilated more than 2 cm, ultrasound will not increase
the accuracy of the prediction for preterm labor and is not indicated.
TRANSDUCER
Transvaginal 3.5–9.0 MHz transducer. (Translabial sonography is an
alternative by using a 3.5–5.0 MHz transducer. However, maternal
bladder should be empty.)
APPEARANCE
The sagittal section of the lower uterine segment and the end of the cervix is taken including the corner of the maternal bladder and amniotic
uid in the uterus.
The internal os, the cervical canal, and the anterior and posterior lip of
the cervix at the external os should be identied.
When an adequate view of the cervix is obtained, the transducer is
withdrawn about 2 cm, to avoid exaggerated lengths.
The length of the closed cervix is measured from the internal to the
external os.
(At least three adequate measurements are obtained, and the shortest
of the measurements is taken. During this measurement, allow a few
minutes to see if a uterine contraction occurs as there can be a dramatic
change in cervical length with a contraction.)
MEASUREMENTS
< 22 weeks 40 mm
22–32 weeks 35 mm
> 32 weeks 30 mm
Length of the cervix and cervical canal in pregnancy
A sagittal view of the cervical canal (between cursors). (Image courtesy of Olivia BensonFadayo)
Between 22 and 30 weeks the 10th percentile for cervical length is
25mm, and a length less than this is signicantly associated with preterm birth.
FURTHER READING
Moroz LA, Simhan HN. Rate of sonographic cervical shortening
and the risk of spontaneous preterm birth. Am J Obstet
Gynecol. 2012; 206:e1–e5.
Taylor BK. Sonographic assessment of cervical length and the risk
of preterm birth. J Obstet Gynecol Neonatal Nursing. 2011;
40:617– 631.
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