c o R R E s PO N D E N c E 29 1

participate and 68% of the cohort were followed up successfully. Four different surgical procedures were considered together which makes it impossible to interpret cure rates and the effect of surgery on the indi- vidual women. Previous continence surgery was not reported and can affect surgical outcome.

The authors have shown no significant difference in outcome between women who had pre-operative urodynamic testing and those who did not. Assuming the objective cure rates reported in the litera- ture?.? two groups of 220 women would be required to show that uro- dynamics did not make a difference to the outcome of surgery, assuming a power of 0.90 and a significance level of 0.05‘. The reported study is too small to demonstrate this. The women who under- went urodynamic investigation may have represented a selected group who had undergone previous continence surgery which is known to reduce the cure rate. The authors state that the improvement measured depended on the pre-operative symptom impact index scores so that women with worse scores initially had the worst scores after surgery. The women who had undergone urodynamics had higher scores than those women who did not. After surgery both groups had similar index scores. The women who had undergone urodynamics may have bene- fitted. The main reason for performing urodynamics is to determine who would benefit from treatments other than surgery and this was not addressed in the current survey.

In this study only 32% of women had moderate or major improve ment one year after surgery; this contrasts with a symptomatic follow up study of women who had undergone incontinence surgery following pre-operative urodynamics. Two hundred and one women were assessed with a postal validated disease specific questionnaire’ before and after colposuspension. Only 39 women (19.4%) had any inconti- nence with 24 (12%) finding that this disturbed their lifestyle to some degree. Of a smaller number of women (n =28) who had undergone an anterior repair only 10 (35.7%) were dry. The greatest contrast between our data and this study were that 96.5% of our women would recom- mend investigation and treatment to their friends, compared with 68% in the reported study‘.

In conclusion the effects of incontinence surgery should be studied with an understanding of the confounding variables which can affect the findings, otherwise the results are not meaningful. The data pre- sented by Black and colleagues may be misleading to those who per- form and those who undergo incontinence surgery.

Vik Khullar, Linda Cardozo, Ann McLellan, John Bidrnead & Con Kelleher llrogynaecology Unit, King’s College Hospital, London

References 1 Black N. Bowling A, Griffiths J, Pope C, Abel P. Impact of surgery for

stress incontinence on the social lives of women. Br J Obstet Gynaecol 1998; 105: 605-612.

2 Stanton SL, Cardozo LD. Results of the colposuspension operation for incontinence and prolapse. BrJ Obsrer Gynaecoll979; 86: 693-697.

3 Colombo M, Zanetta G, Vitobello D, Milani R. The Burch colposuspen- sion for women with and without detrusor overactivity. Br J Obsfet Gynaecoll996; 103: 255-260.

4 Altman DG. How large is a sample? In: Gore SM, Altman DG, editors. Statistics in Practice. London: BMJ Publishing Group, 1982: 6-8.

5 Kelleher CJ, Cardozo LD, Khullar V, Salvatore S. A new questionnaire to assess the quality of life of urinary incontinent women. Br J Obsfet Gynaecoll997; 104: 1374-1379.

6 Black N, Griffiths J, Pope C, Bowling A, Abel P. Impact of surgery for stress incontinence on morbidity: cohort study. BMJ 1997; 315: 1493- 1498.

AUTHOR’S REPLY Sic Khullar and colleagues make several criticisms of our study’. First, they suggest the study is biased because only 47% of the clinicians invited to participate agreed. This may have biased the results but on this line of argument all previous randomised and non-randomised

studies, including the two examples they cite, are likely to be even more biased as they were based on a single hospital’s experience, whereas our study included 18 hospitals. As regards our response rate, we analysed and reported any bias that may have arisen from 68% patient inclusion and showed there was only a slight effect which would have underestimated the effect of surgery on the activities of daily living. As no previous study in this field has reported in such detail on recruitment and response, it is impossible to make any com- parisons.

Secondly, they correctly point out that our study tells them nothing about the relative performance of different procedures. This will be the subject of another paper currently in preparation. Thirdly, they suggest that previous continence surgery affects outcome. About a fifth of the women in our study had undergone surgery before but on multivariate analysis this was not associated with outcome. This will be shown in another paper currently in press’.

Fourthly, they suggest our sample size was too small to demonstrate the benefits of pre-operative urodynamic testing as regards cure (i.e. continence) after surgery. As we did not report this outcome in this paper we assume they are referring to another paper’ in which symp- tom severity is shown to differ by 0.3 (on a scale from 1-20) between those tested and those not. All that a larger sample would achieve is a narrowing of the confidence interval (-1.2 to 1.8). It would not be expected to change the size of the difference. While they are right to suggest that previous surgery could be a confounder, in practice it was not.

Finally, Khullar and colleagues refer to the results of their own study. As this has not yet been published, it is difficult to comment on why their patients apparently had better outcomes than the women in our study. Possibilities are that outcome was assessed sooner after surgery, that the surgeons who participated were better, that patient inclusion was more restrictive, and that the researchers were not independent. Until the study is published the me explanation will remain unknown.

Nick Black Department of Public Health and Policy, London School of Hygiene and Tropical Medicine

References 1 Black N, Bowling A, Griffiths J, Pope. C, Abel P. Impact of surgery for

stress incontinence on the social lives of women. Br J Obsret Gynaecol 1998; 105: 605-612.

2 Hutchings A. Griffiths J, Black N. Surgery for stress incontinence: fac- tors associated with a successful outcome. BJU 1999. In press.

3 Black N. Griffiths J, Pope C, Bowling A. Abel P. Impact of surgery for stress incontinence on morbidity: cohort study. BMJ 1997; 315: 149.3- 1498.

Randomised trial comparing the upright and supine positions for the second stage of labour (Received 6 May 1998)

Sic P.R. de Jong et af. reported a randomised clinical trial of upright and supine positions for delivery which concluded that women delivering upright suffered less perineal trauma (Vol 104, May 1997)’. However, their data show the opposite: women delivering upright had more peri- neal trauma.

Their Table 3 gives odds ratios for intact perineum and perineal trauma needing repair that are both greater than one in the upright group, a logical impossibility. Of 514 women, 257 were allocated to the upright group and 260 to the supine group. Perineal outcomes were repoad for all, presumably including the three who underwent caesarean section, since 514 perineal outcomes are reported. Perineal trauma needing repair was reported in 11 8 upright women and 97 supine women. The actual odds ratio is therefore 1.43 (95% CI 1.W2.03). They reported an odds ratio of 1.42 (95% CI 1.00-2.20). This indicates an increase in trauma in the upright group. Intact perineum was reported in 139 upright

0 RCOG 1999 Br J Obstet Gynaecol 106,286-292