Preterm breech babies and randomised trials of rare conditions

Who's afraid of Thomas Bayes?

Sometimes direct evidence is so strong that a prescription for practice is decreed. Usually, things are not that simple-leaving aside the possibility that important trade offs may be involved, direct comparative data may be imprecise (especially in crucial sub-groups) or subject to possible bias, or there may be no direct comparative evidence; but still decisions have to be made. In these circumstances, indirect evidence-the plausibility of effects-enters the frame. But how should we describe the extent of plausibility and, having done so, how can this be integrated with any direct evidence that might exist. Also, how can allowance be made in a transparent (that is, explicit) way for perceptions of the size of bias in the direct evidence. Enter the Reverend Thomas Bayes; plausibility (however derived-laboratory experiment, qualitative study or just "experience") is captured numerically as degrees of belief ("prior" to the direct data) and updated (by the direct evidence) to yield "posterior" probabilities for use in decision making. The mathematical model used for this purpose must explicitly take account of assumptions about bias in the direct data. This paradigm bridges theory and practice, and provides the intellectual scaffold for those who recognise that (numerically definable) probabilities, and values (also numerically definable) underlie decisions, but who also realise that subjectivity is ineluctable in science.

Elective versus selective caesarean section for delivery of the small baby

BACKGROUND

Elective caesarean delivery for women in preterm labour might reduce the chances of fetal or neonatal death, but it might also increase the risk of maternal morbidity.

OBJECTIVES

The objective of this review was to assess the effects of a policy of elective caesarean delivery versus selective caesarean delivery for women in preterm labour.

SEARCH STRATEGY

The Cochrane Pregnancy and Childbirth Group trials register was searched.

SELECTION CRITERIA

Randomised trials comparing a policy of elective caesarean delivery with expectant management with recourse to caesarean section.

DATA COLLECTION AND ANALYSIS

One reviewer assessed eligibility and trial quality.

MAIN RESULTS

Five studies involving 104 women were included. All trials reported recruiting difficulties. No significant differences between elective and selective policies for caesarean delivery were found for fetal, neonatal or maternal outcomes.

REVIEWER'S CONCLUSIONS

There is not enough evidence to evaluate the use of a policy for elective caesarean delivery for small babies. Randomised trials in this area are likely to continue to experience recruitment problems. However it still may be possible to investigate elective caesarean delivery in preterm babies presenting cephalically.

A randomised trial of mode of delivery in women infected with the human immunodeficiency virus

OBJECTIVE

During the pilot phase of a trial to evaluate the effectiveness of caesarean section delivery compared with vaginal delivery in reducing mother-to-child transmission of human immunodeficiency virus (HIV) infection, the feasibility of randomisation to mode of delivery was assessed.

DESIGN

At 36 weeks of pregnancy, women infected with HIV were randomly allocated to either caesarean section delivery at 38 weeks or vaginal delivery. Information was also collected on the reasons why women were not enrolled, either because they refused or had a contraindication.

SETTING

Fifty-one centres in six European countries.

POPULATION

Pregnant women with confirmed HIV-1 infection.

MAIN OUTCOME MEASURES

Randomisation.

RESULTS

Three-hundred and thirty-nine women had been randomised by the end of 1996, the large majority from Italy (n = 250) and France (n = 54), with 22 from South Africa, three from Sweden, nine from Barcelona and one from London. A further 150 women were eligible but had not been randomised. Forty-eight women (14%) were not delivered according to the arm to which they were randomised; the majority (n = 44) were changed from vaginal to caesarean section delivery. There is wide variation between European countries in the acceptability and adherence to the mode of delivery trial.

CONCLUSION

The pilot phase of this trial has shown that in some settings randomisation to mode of delivery is feasible and acceptable, but that in other settings clinicians and pregnant women are more reluctant to be randomised. Pending further information on transmission rates and accrual, enrollment into the trial continues.