Statistical Analysis
All continuous data were assessed for normality and summary statistics
were reported as mean (standard deviation), median (interquartile range)
or number(percent) as appropriate. Demographics of the women before and
after the guideline was implemented were tabulated compared using either
a t-test, a Kruskal Wallis or chi2 test as
appropriate. The rate of stillbirth per 1000 births before and after the
guideline for south Asian born women and all other women were
determined. The association between the change in clinical practice and
rates of stillbirth was then determined using log linked generalised
linear regression. Adjustment with maternal age, BMI, parity, and
presence of pre-existing medical conditions (pre-existing hypertension,
type 2 diabetes or thyroid disease) or obstetric conditions (gestational
hypertension, pre-eclampsia and gestational diabetes) was also
performed. The rate of stillbirth per ongoing week for south Asian born
and all other women before and after the change in practice was
determined and plotted. Differences in secondary outcomes stratified by
maternal exposure group before and after the change in practice were
also tabulated and compared using standard approaches. When evaluating
the impact of interventions to reduce stillbirth, understanding
potential harms or changes to intervention rates need to be balanced.
The rates of induction of labour are widely acknowledged to be
increasing therefore pooling and comparing rates before and after the
change is not appropriate. Therefore we performed a two-group,
interrupted time-series analysis using Newey-West standard errors and a
lag of 1 to determine the change in rates of induction of labour over
time following the implementation of the guideline, taking into account
the trends in induction over time prior to the guideline between south
Asian and all other women18. We did not correct for
seasonality. All statistics were performed using StataCorp 12.