Inferential statistics
Variables concerning the exposed and reference group were compared using the independent samples T-test, Pearson’s Chi-square test, or Fisher’s exact test whenever applicable.
Regression analyses on the primary (gestational age) and secondary outcomes (birth weight, APGAR scores, congenital malformations, and prolonged psychiatric care) were performed to adjust the study group (BDZ-exposed versus reference group) for confounding variables.
Comparison of baseline characteristics (p<0.05) and univariate regression analyses were performed to select potential confounders. Variables with a p-value <0.1 by univariate analysis were entered in the multivariable regression model for backward regression analysis. Variables with a non-obvious time relationship with the investigated outcome (e.g. epidural/spinal anesthesia and gestational age), were excluded from the multivariable model. All statistical tests were performed using Rstudio.
Ethical approval
The Daily Board of the Medical Ethics Committee Isala Zwolle, The Netherlands, has reviewed this study. As a result, the rules laid down in the Medical Research Involving Human Subjects Act (also known by its Dutch abbreviation WMO), do not apply to this research proposal.
Our findings are reported according to the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guideline.