Statistical analyses
Multiple regressions were used to estimate the effects of prenatal maternal anxiety on birthweight and gestational age. In a full cohort where all subjects with the exposures, outcomes and adjusting variables were included, we regressed birthweight and gestational age on maternal anxiety score at 17th and 30thgestational week, their interactions (Crude in Table 2-A and 2-B), and further included adjusting variables step by step. The step1 encompassed maternal smoking and alcohol intake, and the step 2 was those in the step 1 and parity, birth complication, child’s sex and preeclampsia. The step 3 was those in the step 2 and maternal age, education and marital status. Regression analyses were performed in R 4.0.0.
In the sibling comparison design, we selected all available sibling pairs (For families participating more than three times, the sibling pairs were randomly selected) and computed the difference values in each variable between a sibling and the other. Similar to the analyses in the full cohort, we regressed the sibling-difference values in the outcomes on those in the exposures, controlling for family shared effects. Here, the three steps of adjustments were made in the same manner as in the full cohort.
We performed multiple imputations to handle the missing data points in the exposures, outcomes and adjusting variables. The mice R package was used; the number of imputations was set to be 5 (m=5), and the imputation method in use was predictive mean matching (method=“pmm”). All the analyses in the full cohort and sibling-design were re-run using the imputed data (Supplementary File x).