Supplementary analyses after multiple imputations
Additional supplementary analyses was conducted after multiple imputations. As can be seen in the supplementary files S-Table 2-A and S-Table 2-B, after multiple imputations the width of the confidence intervals was smaller. In addition the association between prenatal maternal anxiety at week 30 and gestational age remained in the sibling cohort, adjusting for shared family effects and control variables in all steps.