Statistical analysis
Where data permitted, Stata 14 was used to conduct meta-analyses of proportions using a random-effects model. We analysed the available data from three main population groups. The ‘treated’ group were women with CID who required treatment with biologic medications throughout their pregnancy. The ‘disease matched’ group were the group of women with CID not prescribed biologics in pregnancy. The ‘disease free’ group was a group representative of the general population, (i.e. women who were pregnant and did not have a diagnosis of CID). We modelled data using the program metaprop which augments the metan program. This allowed for computation of 95% confidence intervals16and pooling of proportions, presenting a weighted sub-group and overall pooled estimates with inverse-variance weights from a random effects model. The primary analysis was performed on all eligible studies, with subgroup analyses by biologic type and by chronic inflammatory disease subtype where appropriate. We used linear regression analysis to compare the mean of proportions of outcomes across exposure groups using the ‘treated’ group as the reference category.