Endgames Statistical Question

What are the odds?

BMJ 2015; 350 doi: https://doi.org/10.1136/bmj.h2327 (Published 01 May 2015) Cite this as: BMJ 2015;350:h2327
  1. Philip Sedgwick, reader in medical statistics and medical education
  1. 1Institute for Medical and Biomedical Education, St George’s, University of London, London, UK
  1. p.sedgwick{at}sgul.ac.uk

Researchers investigated the effects of adding an oxytocin infusion to bolus oxytocin on blood loss during elective caesarean sections. A double blind placebo controlled randomised trial was performed. The intervention was bolus oxytocin (intravenous slow 5 IU oxytocin bolus over one minute) and infusion oxytocin (additional 40 IU oxytocin infusion in 500 mL of 0.9% saline solution over four hours). The control treatment was bolus oxytocin (5 IU oxytocin bolus over one minute) and placebo infusion (500 mL of 0.9% saline solution over four hours). The setting was five maternity hospitals in the Republic of Ireland. Participants were women aged over 18 years with a singleton pregnancy who were booked for elective caesarean section at term. In total, 2069 women were recruited and randomised to the intervention (bolus and infusion; n=1037) or control (bolus and placebo infusion; n=1032). Of those women allocated to the intervention, 1007 completed treatment, as did 994 of those allocated to control.1

The primary outcome measures included major obstetric haemorrhage (blood loss >1000 mL) and the need for an additional uterotonic agent. In the intervention group, 158 (15.7%) women experienced a major obstetric haemorrhage, whereas 849 did not. In the control group, 159 (16.0%) women experienced a major obstetric haemorrhage, whereas 835 did not. The unadjusted odds ratio for the occurrence of a major obstetric haemorrhage for the intervention compared with the control was 0.98 (95% confidence interval 0.77 to 1.24; P=0.85). When adjusted for hospital and previous caesarean section, the odds ratio was 0.98 (0.77 to 1.25; P=0.86). The need for an additional uterotonic agent was significantly lower in the intervention group than …

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