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.