OBJECTIVE: To determine whether the rate of instrumental birth in nulliparous women using epidural analgesia is affected by maternal position in the passive second stage of labour. DESIGN: A pragmatic prospective randomised trial. SETTING: Consultant maternity unit in the Midlands. PARTICIPANTS: One hundred and seven nulliparous women using epidural analgesia and reaching the second stage of labour with no contraindications to spontaneous birth. INTERVENTIONS: The lateral versus the supported sitting position during the passive second stage of labour. MEASUREMENTS: Mode of birth, incidence of episiotomy, and perineal suturing. FINDINGS: Recruitment was lower than anticipated (107 versus 220 planned). Lateral position was associated with lower rates of instrumental birth rate (lateral group 33%; sitting group 52%; p = 0.05, RR 0.64, CI for RR 0.40 to 1.01; Number-needed-to-treat (NNT) 5), of episiotomy (45% versus 64%; p = 0.05, RR 0.66, CI for RR 0.44 to 1.00, NNT 5), and of perineal suturing (78% versus 86%; p = 0.243, RR 0.75, CI for RR 0.47 to 1.17). The odds ratio for instrumental birth in the sitting group was 2.2 (CI 1.0 to 4.6). Logistic regression of potential confounder variables was undertaken, due to a large variation in maternal weight between the randomised groups. Of the nine possible confounders tested, only position of the baby's head at full dilation affected the risk of instrumental birth significantly (p = 0.4, OR 2.7 where the fetal head was in the lateral or posterior position). Maternal weight did not appear to have any effect. The odds ratio for instrumental delivery for women randomised to the sitting position was slightly higher within the logistic regression model (adjusted OR 2.3). KEY CONCLUSIONS: Women randomised to the lateral position had a better chance of a spontaneous vaginal birth than those randomised to the supported sitting position. Position of the babies head at full dilation had an additional effect on mode of birth. These effects are not conclusively generalizable. RECOMMENDATIONS FOR PRACTICE: The lateral position is likely to be at best beneficial, and at the worst no less harmful than the sitting position for most women and their babies who meet the criteria set for this study. Conclusive evidence for or against the technique should be established using larger trials.

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