Sonography of the cervix at
Sonography of the cervix at term gestation.
Thesis University Utrecht. With a summary in Dutch.
Author: M. Meijer-Hoogeveen
Cover illustration: woman in labour, Temple of Kom Ombo, Egypt, by Sander Meijer 2003
Design, lay out and printed by Gildeprint Drukkerijen B.V., Enschede
© M. Meijer-Hoogeveen, Zeist, 2007
All rights reserved. No part of this thesis may be reproduced or transmitted in any form or
by any means, without permission of the copyright owner.
Publication of this thesis was sponsored by the Division Woman and Baby, University Medical
Center, Utrecht; Ferring BV; Toshiba Medical Systems Europe.
Sonography of the cervix at term gestation
Echoscopie van de cervix in de à terme
(met een samenvatting in het Nederlands)
ter verkrijging van de graad van doctor aan de Universiteit Utrecht op gezag van
de rector magnifi cus, prof.dr. W.H. Gispen, ingevolge het besluit van het college
voor promoties in het openbaar te verdedigen op donderdag 14 juni 2007 des
middags te 12.45 uur
geboren op 19 december 1975 te Amstelveen
Co-promotor: Dr. Ph. Stoutenbeek
Prof. dr. G.H.A. Visser
Het is goed een doel te hebben,
maar vergeet niet onderweg te genieten
Aan mijn lieve man en dochter
Table of contents
Chapter 1 Introduction and outline of the thesis 9
Methods of sonographic cervical length measurement
in pregnancy: a review of the literature
Dynamic cervical length changes; preliminary observations
from 30 minutes transvaginal ultrasound recordings
Transperineal versus transvaginal sonographic cervical length
measurement in preterm and term pregnancy
Sonographic longitudinal cervical length measurements in
nulliparous women at term; prediction of spontaneous onset
Prediction of the outcome of labour induction at term by
transvaginal ultrasound in supine and upright position
Prediction of spontaneous onset of labour by transvaginal
ultrasound of the cervix and Bishop Score at prolonged
Prediction of the mode of delivery in women with a previous
caesarean section by transvaginal ultrasound of the cervix
Summary and conclusions
List of abbreviations
List of co-authors
List of publications
Prof. dr. W.P.Th.M. Mali
Prof. dr. H.W. Bruinse
Prof. dr. J.M.G. van Vugt
Prof. dr. K.G.M. Moons
Dr. R.H. Stigter
The cervix consists mainly of connective tissue, containing collagen and elastin and 10-
15% smooth muscle. During pregnancy the fi rm cartilage-like consistency of the cervix is
transformed to soft tissue. A decrease in collagen concentration and an increased elastin/
collagen ratio soften the rigid structure of the cervix. This transformation may be initiated
long before term. This transformation is called “cervical ripening” and enables the cervix
to dilate and facilitate parturition1.
In 1960, the Bishop Score was introduced to assess cervical ripeness before induction of
labour2. The Bishop Score is determined by digital examination, and consists of fi ve different
aspects of the cervix, namely dilatation, effacement, consistency, position and station of
the presenting part of the fetus. Since then, also assessment of preterm cervical ripeness
and cervical incompetence is determined by the Bishop Score.
Only recently, in the nineteen eighties, the usefulness of transvaginal sonography (TVS) of
the cervix for the detection of cervical incompetence became apparent3;4. The advantages
of TVS compared to digital examination of the cervix were recognized shortly after its
introduction. Early cervical ripening, resulting in changes at the internal cervical os, can
be observed by TVS, even in the absence of dilatation. Nowadays, it is considered to be
reproducible5-7 and easy to learn, even for inexperienced investigators8. This has resulted in
a worldwide search for the optimal clinical implementation of this diagnostic tool.
TVS of the cervix is now widely used as a screening method for preterm delivery in
symptomatic and asymptomatic women. Women with symptoms of preterm labour benefi t
most from screening by TVS. When cervical length (CL) on TVS is shorter than 15mm, 40-47%
of these women will deliver within 7 days, irrespective of the use of tocolysis. In contrast,
a CL ≥15mm is reassuring since less than 1-2% will deliver within 7 days9;10.
In asymptomatic women, TVS of the cervix is most benefi cial for the identifi cation of women
at low risk for preterm delivery11. However, a short cervix at mid-gestation ultrasound
does increase the risk of preterm delivery in this group. Although cut-off points vary
between different studies, a CL smaller than 25mm is the most commonly used threshold
to detect women at risk for preterm delivery (OR 4.40; 95% CI 3.53;5.49)12. A cerclage may
prevent preterm delivery, especially in women with a history of cervical incompetence
or preterm delivery13. When a CL smaller than 25mm is found in women at high risk for
preterm delivery, a cerclage in combination with bed rest may decrease the prevalence of
preterm delivery compared to bed rest alone. In one Dutch study the prevalences were 44
and 1% respectively14. A shorter cut-off for CL probably identifi es women at high risk more
accurately, but may increase the risk of ascending infection after the procedure15.
In the latest two decades, the clinical use of TVS of the cervix has further been expanded.
There was need for a way to predict the outcome of labour induction at term more accurately
than by the Bishop Score. In several studies pre-induction assessment of cervical ripeness by
TVS has been compared with digital examination, but so far results are confl icting.
It is striking that with the rapid evolvement of TVS in general clinical practice, only a
few small studies report on physiological changes of the cervix preceding term labour.
Knowledge of the physiology of the cervix at term is necessary to interpret TVS results in
case of threatened preterm labour or before induction of labour at term.
AIM AND OUTLINE OF THE THESIS
It is the general objective of this thesis to study the cervix by TVS at term to obtain more
insight in physiological changes preceding parturition, and to relate these changes or
otherwise to the onset and course of spontaneous labour and to the need for and outcome
of induced labour.
This thesis aims to answer the following questions:
1-What is the “gold standard” to obtain optimal cervical measurements by real time
ultrasound, which are the pitfalls and what is the relevance of the different cervical
parameters? This is addressed in a literature review (chapter 2).
2-What are the fl uctuations in CL and which factors cause fl uctuations? This was studied by
performing continuous TVS of the cervix for 30 minutes (chapter 3).
3-How reliable are transperineal CL measurements at term gestation? In case of preterm
rupture of the membranes (PROM) or reluctance with transvaginal examination it may be
relevant to have a reliable substitute for the transvaginal approach. Literature has shown
that transperineal CL measurements can be used reliably during the preterm period. We
have investigated this at term (chapter 4).
4-Which are the cervical changes that precede spontaneous onset of labour at term and can
the timing of labour be predicted by CL measurements? This was studied in a homogenous
nulliparous population by serial TVS of the cervix from 36 weeks of gestation onwards
(chapter 5). Furthermore, the effect of a maternal postural change (from supine to upright
position) on the predictive value of the CL measurements was studied.
5-Do pre-induction CL measurements in either supine or upright position predict the outcome
of labour induction at term better than the Bishop Score? Previous studies on the prediction
of success after labour induction appear to be contradictive (chapter 6).
6-Can TVS of the cervix or the Bishop Score predict spontaneous onset of labour beyond 41
weeks of gestation? This might be helpful in the decision for either induction of labour or
expectant management at prolonged pregnancy. We studied nulliparous women, who have
a higher risk of failed induction than parous women (chapter 7).
7-Can women at high risk for a repeat caesarean section (CS) be detected by CL measurements?
For this purpose we studied women with a previous CS for failure of progress or breech
presentation. Serial TVS of the cervix was performed from 36 weeks of gestation onwards
(chapter 8), in order to detect differences between women who delivered vaginally and
those who needed a repeat CS.
In Chapter 9 the results are summarized and recommendations for clinical use are given.
1. Leppert PC. Anatomy and physiology of cervical ripening. Clin.Obstet.Gynecol. 38, 267-
2. BISHOP EH. Induction of labor. GP. 21, 96-101. 1960.
3. Jackson G, Pendleton HJ, Nichol B, Wittmann BK. Diagnostic ultrasound in the assessment of
patients with incompetent cervix. Br.J.Obstet.Gynaecol. 91, 232-236. 1984.
4. Michaels WH, Montgomery C, Karo J, Temple J, Ager J, Olson J. Ultrasound differentiation
of the competent from the incompetent cervix: prevention of preterm delivery.
Am.J.Obstet.Gynecol. 154, 537-546. 1986.
5. Burger M, Weber-Rossler T, Willmann M. Measurement of the pregnant cervix by transvaginal
sonography: an interobserver study and new standards to improve the interobserver
variability. Ultrasound Obstet.Gynecol. 9, 188-193. 1997.
6. Lazanakis M, Marsh M, Brockbank E, Economides D. Assessment of the cervix in the third
trimester of pregnancy using transvaginal ultrasound scanning. Eur.J.Obstet.
Gynecol.Reprod.Biol. 105, 31-35. 2002.
7. Valentin L, Bergelin I. Intra- and interobserver reproducibility of ultrasound measurements of
cervical length and width in the second and third trimesters of pregnancy. Ultrasound
Obstet.Gynecol. 20, 256-262. 2002.
8. Vayssiere C, Moriniere C, Camus E, Le Strat Y, Poty L, Fermanian J, Ville Y. Measuring cervical
length with ultrasound: evaluation of the procedures and duration of a learning
method. Ultrasound Obstet.Gynecol. 20, 575-579. 2002.
9. Tsoi E, Akmal S, Rane S, Otigbah C, Nicolaides KH. Ultrasound assessment of cervical length
in threatened preterm labor. Ultrasound Obstet.Gynecol. 21, 552-555. 2003.
10. Fuchs IB, Henrich W, Osthues K, Dudenhausen JW. Sonographic cervical length in singleton
pregnancies with intact membranes presenting with threatened preterm labor.
Ultrasound Obstet.Gynecol. 24, 554-557. 2004.
11. Rozenberg P, Gillet A, Ville Y. Transvaginal sonographic examination of the cervix in
asymptomatic pregnant women: review of the literature. Ultrasound Obstet.
Gynecol. 19, 302-311. 2002.
12. Honest H, Bachmann LM, Coomarasamy A, Gupta JK, Kleijnen J, Khan KS. Accuracy of cervical
transvaginal sonography in predicting preterm birth: a systematic review. Ultrasound
Obstet.Gynecol. 22, 305-322. 2003.
13. Berghella V, Odibo AO, To MS, Rust OA, Althuisius SM. Cerclage for short cervix on
ultrasonography: meta-analysis of trials using individual patient-level data. Obstet.
Gynecol. 106, 181-189. 2005.
14. Althuisius SM, Dekker GA, Hummel P, Bekedam DJ, van Geijn HP. Final results of the Cervical
Incompetence Prevention Randomized Cerclage Trial (CIPRACT): therapeutic
cerclage with bed rest versus bed rest alone. Am.J.Obstet.Gynecol. 185, 1106-
15. Althuisius SM. The short and funneling cervix: when to use cerclage? Curr.Opin.Obstet.
Gynecol. 17, 574-578. 2005.
Methods of sonographic cervical length measurement
in pregnancy: a review of the literature
Gerard H.A. Visser