Academic Department of Obstetrics & Gynaecology, University of Hull, Hull Maternity Hospital, Hull, UK
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Abstract |
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Key words: cerclage/cervix/pregnancy
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Introduction |
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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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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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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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Discussion |
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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 12 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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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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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, 471476.[ISI][Medline]
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Submitted on March 17, 2000; accepted on October 2, 2000.