Human Reproduction, Vol. 16, No. 1, 172-173,
January 2001
© 2001 European Society of Human Reproduction and Embryology
Reversal of asymptomatic cervical length shortening with cervical cerclage: a preliminary study
Academic Department of Obstetrics & Gynaecology, University of Hull, Hull Maternity Hospital, Hull, UK
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Abstract |
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This is a prospective observational study which highlights the value of serial transvaginal cervical length measurements to identify asymptomatic cervical length shortening and the effect on cervical length following insertion of a McDonald cerclage. Four out of 14 patients exhibited asymptomatic cervical length shortening. Only patients whose cervical length was <2 cm underwent cerclage. All patients showed an increase in cervical length post-cerclage. The possible mechanisms responsible for these changes are discussed.
Key words: cerclage/cervix/pregnancy
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Introduction |
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The accurate prediction and subsequent prevention of preterm delivery remains an enigma. Ultrasound assessment of the cervix during pregnancy appears to offer an opportunity to understand the pathogenesis of preterm labour. In the last decade an apparent shortening of the cervix with increasing gestation has been described (Guzman et al., 1996
; Iams et al., 1996). The likelihood of preterm delivery increases with decreasing cervical length at 24–28 weeks gestation (Iams et al., 1996). A cervical length of 25–30 mm before 32 weeks gestation and/or funnelling of the internal os constituting 40–50% of the total cervical canal have emerged as the two factors associated with an increased risk of preterm delivery (Berghella et al., 1997).
Transvaginal ultrasound evaluation of the cervix in pregnancy has dispelled the `all or nothing' concept of cervical competence and it has been postulated that cervical competence is a continuum (Iams et al., 1995).
Traditionally, cervical cerclage has been performed either electively (based on past obstetric performance) or as an emergency procedure in patients presenting in early labour who respond to tocolytic treatment. A new category of patient may benefit from cervical cerclage, namely the patient who exhibits cervical shortening and/or funnelling of the internal os on ultrasound assessment of the cervix in the mid trimester (Kurup and Goldkrand, 1999).
The aim of this study was to evaluate the therapeutic effect of McDonald cerclage (McDonald, 1957) on this new category of patient as assessed by serial transvaginal ultrasound.
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Materials and methods |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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A prospective observational study was conducted. Women with a past obstetric history of preterm delivery were recruited. All patients gave written informed consent. Each patient underwent serial transvaginal ultrasound cervical assessment (cervical length measurements and assessment of funnelling) and serial microbiological evaluation of the vagina. The cervical length was measured by placing markers at the furthest points at which the cervical canal walls were juxtaposed. Funnelling was described in terms of cervical shape, namely U-shaped or V-shaped. The depth and width of the funnelling was also measured. All ultrasound measurements were made by experienced ultrasonographers. Two transvaginal scans were performed 24 h apart to ensure a true evaluation of cervical shortening prior to performing cerclage. Repeat ultrasound evaluations were made at 1 week post-operation.
Of the 14 high-risk patients who underwent serial transvaginal ultrasound scanning, four patients exhibited asymptomatic cervical shortening and/or funnelling and underwent an urgent McDonald cerclage (Table I).
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Results |
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Four patients at a mean gestation of 24.25 weeks underwent a cervical cerclage. The mean (SD) pre- and post-cerclage cervical length was 1.46 (0.48) cm and 2.45 (0.58) cm, a statistically significant difference (P = 0.036, paired t-test). Expressed as a percentage of the pre-cerclage length, the mean increase was 80.75% (range 17–153) (Table I
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When categorized with respect to the normal distribution of cervical length at 24 weeks gestation (Iams et al., 1996), the patients who underwent cerclage demonstrated a change in percentiles before and subsequently after cerclage of approximately 10 percentiles (Figure 1).
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The mean cerclage–delivery interval was 68 days (range 12–112). One patient went into spontaneous labour at 12 days post-cerclage; the other three patients underwent LSCS (lower segment Caesarean section) before labour, two at 38 weeks and one at 34 weeks gestation.
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Discussion |
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This is the first study whose aim was to perform serial transvaginal cervical length measurements to identify asymptomatic cervical shortening and to assess the effect of a McDonald cerclage.
All our cerclages were inserted following a measured shortening of the cervical length on transvaginal ultrasound. The cervical length pre-operatively was <2 cm in all cases. We have demonstrated, like others (Guzman et al., 1996; Funai et al., 1999; Althuisius et al., 1999), an increase in cervical length as measured by transvaginal ultrasound post-cervical cerclage.
The mechanism responsible for the increase in length post-cerclage is not known. Some have suggested that it may be due to the cerclage merely obliterating the funnelling and so give an apparent increase in cervical length. While we accept that this is a possibility, we feel that as funnelling persisted in all our patients post-cerclage, there must be some other mechanism at play. The closure of the cervical canal above the suture may be an important mechanism of action of an effective cerclage. It is possible that the cerclage constitutes an effective bacteriological barrier to vaginal bacteria (Jones et al., 1998). None of our patients had a positive culture for pathological vaginal bacteria either pre- or post-cerclage. Alternatively or concurrently the suture may inhibit the propagation of uterine contractions transmitting pressure to the cervix. A third possibility is that the suture creates ischaemia in the cervical tissues which alters the responsiveness to circulating hormones (e.g. oestrogen), or a local response to the endogenous production of prostaglandins.
Serial ultrasound evaluation of the cervix has not been thoroughly evaluated but these data indicate a shortening period of approximately 1–2 weeks.
Our study demonstrates the value of serial transvaginal ultrasound of the cervix in a high risk group to identify asymptomatic cervical shortening and an increase in cervical length post-McDonald cerclage, with a resultant prolongation of pregnancy; however the study is small and so it is not possible to draw firm conclusions. The results clearly warrant a randomized controlled trial of serial transvaginal ultrasound of the cervix in patients with a previous history of preterm labour, with the aim of evaluation of a therapeutic intervention using cervical cerclage in those with asymptomatic cervical shortening.
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Notes |
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1 Present address: Assistant Master, Maternity Hospital, Holles Street, Dublin 2, Republic of Ireland
2 To whom correspondence should be addressed at: Academic Department of Obstetrics & Gynaecology, University of Hull, Hull Maternity Hospital, Hedon Road, Hull HU9 5LX, UK
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References |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Althuisius, S.M., Dekker, G.A., van Geijn, H.P. and Hummel, P. (1999) The effect of therapeutic McDonald cerclage on cervical length assessed by transvaginal ultrasonography. Am. J. Obstet. Gynecol., 180, 366–370.[Medline]
Berghella, V., Kuhlman, K., Weiner, S. et al. (1997) Cervical funneling: sonographic criteria predictive of preterm delivery. Ultrasound Obstet. Gynecol., 10, 161–166.[Medline]
Funai, E.F., Paidas, M.J., Rebarber, A. et al. (1999) Change in cervical length after prophylactic cerclage. Obstet. Gynecol., 94, 117–119.[Medline]
Guzman, E.R., Houlihan, C., Vintzileos, A. et al. (1996) The significance of transvaginal ultrasonographic evaluation of the cervix in women treated with emergency cerclage. Am. J. Obstet. Gynecol., 175, 471–476.[Medline]
Iams, J.D., Johnson, F.F., Sonek, J. et al. (1995) Cervical competence as a continuum: A study of ultrasonographic cervical length and obstetric performance. Am. J. Obstet. Gynecol., 172, 1097–1106.[Web of Science][Medline]
Iams, J.D., Goldenburg, R.L., Meis, P.J. et al. (1996) The length of the cervix and the risk of spontaneous delivery. N. Engl. J. Med., 334, 567–572.
Jones, G., Clark, T. and Bewley, S. (1998) The weak cervix: failing to keep the baby in or infection out? Br. J. Obstet. Gynaecol., 105, 1214–1215.[Medline]
Kurup, M. and Goldkrand, J.W. (1999) Cervical incompetence: elective, emergency, or urgent cerclage. Am. J. Obstet. Gynecol., 181, 240–246.[Medline]
McDonald, I.A. (1957) Suture of the cervix for inevitable miscarriage. J. Obstet. Gynaecol. Br. Empire, 64, 346–350.[Medline]
Submitted on March 17, 2000; accepted on October 2, 2000.
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