Clarifying the ‘weekend effect’

In November 2015, a study on the association between day of delivery and obstetric outcomes caught the headlines (Palmer et al, 2015). There is a risk that some of the more shockingly worded headlines could create unnecessary anxiety. Recognising this, the authors would like to clarify what the paper did and did not say, which will hopefully help midwives to understand the research and, if necessary, explain the implications to pregnant women and their families.

The study was based on 2 years of NHS data (up to March 2012) covering some 1.3 million births. We looked to see whether there was an association between day of delivery—in particular, weekday versus weekend—and outcomes, namely perinatal mortality and (for both infant and mother) infections, emergency readmissions, and injuries. We used analytical techniques to control for differences in the complexity of each birth where data were available, such as delivery method, birth weight, gestational age and maternal age. In the paper, we also set out the key limitations of the approach, including incomplete data on case mix and difficulties in categorising the births by day.