Correspondence tering and electrode placement on the ECG waveform and have recently studied 46 fetuses (unpublished) using bandwidth filtering of between 0-05and 150 Hz with active electrodes on the fetal head and maternal thigh as recommended by Lindecrantz et al. (1988). The average T/QRS ratio was 10% during the seven normal labours, as we found previously (Newbold et al. 1989). No increase in the T/QRS ratio was seen in the one fetus in this group with a fetal metabolic acidosis at delivery (cord artery pH 7.15, delta base deficit 4-2 mmolfl). The large database of Goldaber et al. (1991)is used by Westgate and Greene to suggest that a suitable cut-off for ‘clinically significant acidaemia’ is a cord artery pH C7.05. At this level the incidence, for example, of neonatal intubation was 19.4% and of neonatal seizures 6.6%. Fetal monitoring should not only inform the clinician that this possibility has arisen but also provide an earlier warning that it might develop. In this respect the value of measuring the T/QRS ratio remains to be defined but our data suggest that the development of anaerobic myocardial metabolism sufficient to cause detectable changes in the T/QRS ratio does not

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arise until the pH is notably low. We accept that our study was based upon a small, selected population and that the place of fetal ECG waveform analysis during labour will only become evident when considerably larger series are reported. S. Newbold T. Wheeler Obstetrics and Gynaecology Faculty of Medicine University of Southampton F. Clewlow Department of Medical Engineering Southampton General Hospital

References Goldaber K . , Gilstrap L., Leveno K. & Dax J. (1991) Pathological fctal acidemia. Am J Obster Gynecol 164,251. Lindecrantz K., Lilja H., Widemark C. et 41. (1988) Fetal ECG during labour: a suggestcd standard. J Biomed Eng 10,351-353. Newbold S . , Whccler T.,Clewlow F. & Soul F. (1989) Variation in thc TlQRS ratio of fetal electrocardiograms recorded during labour in normal subjects. Br J Obstet Gynaecol%, 144-150.

British Journal of Obstetrics and Gynaecology October 1991, Vol. 98, pp. 1059-1060

A randomized controlled amniotomy

trial of

early

Dear Sir, We read with interest the article by Fraser et al. [ B r J Obstet Gynaecol(1991)98,84-911 in which the authors failed to demonstrate a significant reduction in the duration of labour following early amniotomy. Several points arise from the article. First, as was noted, the power of the study was inadequate to demonstrate a reduction in labour duration of 20%. Second, an active policy of acceleration with oxytocin was pursued if there was arrest of cervical dilatation for 2 h. The use of oxytocin in controls (i.e., women who did not have an early amniotomy) was 27.6% compared with 30.9% in the amniotomy group. Such a high rate of oxytocin use may have obscured any differential effects of early amniotomy on the duration of labour.

Thirdly, the operative delivery rate was high (17% caesarean sections and 31% forcepdventouse deliveries in the amniotomy group and 8% caesarean sections and 36% forcepdventouse deliveries in the control group). These interventions may also have have shortened the duration of labour artificially. We agree with Fraser et al. that results from large multicentre trials are awaited with interest. In the United Kingdom over 1200 patients have been entered by six participating hospitals into the European Community trial but more are needed. An estimated 2OO04000 patients are required for the study to have sufficient power to show important differences in operative delivery rates and labour duration, and many more to examine fetal outcomes. Psychological aspects of the mothers’ views of labour and the economic consequences of differing labour ward practices are also being studied. We would

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Correspondence

encourage other centres to consider participating. Further details may be obtained from Jim Thornton. M. Tasker C. P. Verduijn C. Bassett K. Murray Tameside Generul Hospital Ashton-under-Lyne Luncashire OL6 YRW J. Thornton St. James’s University Hospital Leeds LSY 7TF Reference Frascr W. D., Sauve R., Parboosingh 1. J . , Fung T. Sokol R. & Prcsaud D. (1991) A randomized controlled trial of early amniotomy Br J Obsrer GynaeCOI 98, 84-91. Author’s reply Dear Sir,

I welcome the comments made by Drs Tasker et al., as I fcel it is important to attempt to understand the discrcpancy between the findings of our study and previous studies. As noted in the original manuscript, the power of the study to detect a rcduction in labour duration of 20% was only 0.55. The study had adequate power to detect reductions in labour duration of 30% or more. Regarding the frequcncy of use of oxytocin in the context of thc study, it must be emphasized that the objective of the study was to assess the effectof differing policies of membrane management within a specific clinical context. Although the frequency of oxytocin usc obscrved in the study may seem to bc high, this pattern reflects the practice observed in a large number of teach-

ing and community hospitals in Canada. It would seem appropriatc to assess the effect of oxytocin within a clinical context which is representative of current obstetric practice. The commcnts relating to operative dclivcry rates observed in thc study are worthy of considcration. In fact, the analysis of labour duration included only thc women delivered vaginally. The cffect of operative vaginal delivery on labour duration was likely balanced in the two treatment groups as the frequency of forceps use was similar. An effect of amniotomy on the duration of labour would be most likely to be observed during the interval between randomization and full dilatation. When a post-hoc powcr analysis was done in relation to this interval (again for subjects delivered vaginally) the study powcr was 0-85 for an effect size of 0.7 (2-tailed). As mentioned in the original article, approximately one half of the women in the study were randomizcd whcn the cervical dilatation was less than 3 crn. It is my suspicion that the discrepancy between thc rcsults of the present and previous studies of amniotomy may be due to differences in the distribution of cervical dilatation at the time of randomization. We are currently completing a clinical trial of YO0 nulliparous women in which randomization is prospectively stratified by cervical dilatation at randomization (

A randomized controlled trial of early amniotomy.

Correspondence tering and electrode placement on the ECG waveform and have recently studied 46 fetuses (unpublished) using bandwidth filtering of betw...
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