Data analysis
Each reported cause of stillbirth was mapped to the relevant
International Classification of Disease of perinatal mortality
(ICD-10-PM) category. The ICD-PM includes five major maternal conditions
categories (M1-5) and thirteen foetal categories, six with antepartum
timing (A1-6), seven with intrapartum timing (I1-7), and others with
unknown timing. For the Unknown (U) timing category, we included those
categories described previously for consistency. Categories of
stillbirth causes were represented as proportions of the total number of
stillbirths for various ethnicities. Results for each ethnicity from
different studies were statistically pooled using random effects
meta-analysis using the metaprop command in STATA (version 16,
Stata Corp, TX, USA) for binomial data. Pooled estimates were calculated
after Freeman-Tukey double arcsine transformation of data to stabilise
the variances and enable studies with estimated proportions of 0 or 1 to
be retained.15 I 2 values were
not reported as measures of heterogeneity as such statistics may be less
informative in meta-analyses of cohort/observational studies where
sample sizes are relatively large and the within-study variation
correspondingly small.16 Data were tabulated as pooled
estimate of proportion (95% confidence interval).