Statistical analyses
Data analysis was carried out using Review Manager (version 5.3)
software. Heterogeneity between studies was explored using the Higgins
I2 statistics. When there was substantial
heterogeneity (I2 ≥ 50%),
the random effect model was used to
estimate the pooled risk ratio, otherwise the fixed effect model was
used. Subgroup analyses were employed
to evaluate the sources of heterogeneity, and stratification by twin
chorionicity (DC and MC) was performed to exclude the impact of
chorionicity on the outcome. The odds ratio (OR) and 95% confidence
interval (CI) were the summary measures applied to assess each endpoint.
Potential publication biases were statistically examined by Egger’s test
and visually by funnel plots (Figure S2).