CERVICAL LENGTH IN PREGNANCY  

There is a wide variation in the length of the cervical canal when measured transabdominally with a full bladder. Overdistention of the bladder gives one the impression that the cervix is elongated due to compression of the anterior and posterior uterine wall. Similarly an empty bladder results in the cervix being more vertically orientated and falsely short.

Transvaginal scanning avoids the problem cervical distortion and is probably the most accurate method.

The normal mean cervical length is >3 cm until 32-34 weeks of gestation. Thereafter gradual shortening and effacement occurs. There is no significant difference in the cervical length of primigravid and multigravid women (1,2). Progressive shortening of the cervix is more significant than a single abnormal cervical length measurement (3).
 

Ref.

Maternal Bladder

Mean Length
(mm)

1 SD
(mm)

Gestational
Age (wks)

(1)
(2)
(4)
(5)
(6)
(7)

Distended
Empty (TVS)
Distended
Distended
Distended
Partially Distended
Empty TAS

52.0
45.0
37.0
35.0
48.0
46.0
32.5

6.0
4.9
Na
4.3
3.4
Na
Na

8-33
8-31
<12-40
10-36
10-28
8-35
8-35

 

 

REFERENCES
  1. Ayers JW, DeGrood RM, Comptin AA et.al. Sonographic evaluation of cervical length in pregnancy: diagnosis and management of preterm cervical effacement in patients at risk for premature delivery. Obstet Gynecol 1988;71:939-944.
  2. Kushnir O, Vigil DA, Izquierdo L et.al. Vaginal ultrasonographic assessment of cervical length changes during normal pregnancy. Am J Obstet Gynecol 1990;162:991-993.
  3. Michaels WH, Montgomery C, Karo J et.al. Ultrasound differentiation of the competent from the incompetent cervix: prevention of preterm delivery. Am J Obstet Gynecol 1986;154:537-546.
  4. Zemlyn S. The length of the uterine cervix and its significance. J Clin Ultrasound 1981;9:267-269.
  5. Varma TR, Patel RH, Pillai U. Ultrasonic assessment of cervix in normal pregnancy. Acta Obstet Gynecol Scand 1986;65:229-233.
  6. Podobnik M, Bulic M, Smiljanic M et.al. Ultrasonography in the detection of cervical incompetence. J Clin Ultrasound 1988;16:383-391.
  7. Bowie JD, Andreotti RF, Rosenberg ER. Sonographic appearance of the uterine cervix in pregnancy. AJR 1983;140:737-740.