Statistical analyses
Characteristics were compared between case and control mothers.
Descriptive statistics of the study population were presented using
means and standard deviations for normal distributed variables and
median and interquartile range for skewed variables. Analysis was
performed by Student t test and Mann-Whitney U test,
respectively. Frequencies (proportions), were used for categorical
variables and were compared by chi-square test.
Spearman correlations was used to evaluate correlations between maternal
age, and homocysteine, and TL.
Multivariable logistic regression was used to compute crude and adjusted
odds ratios (OR) per standard deviation (SD) decrease between the
maternal T/S ratio with 95% confidence intervals (95% CI) and COD and
VSD risk in offspring. The ORs were adjusted for maternal age, as known
confounder for TL and COD (model 1). In a second model, we additionally
adjusted for maternal body-mass-index, ethnicity, education and use of
alcohol or smoking during pregnancy based on the characteristics of the
two study populations and literature.(17, 18) Since homocysteine is an
important oxidative stress marker, the analyses were also performed
after adjustment for homocysteine concentrations.
Probability values ≤ 0.05 were considered statistically significant. All
analyses were performed with R (R for Windows, version 3.5; R Core
Team).
Funding The Bo Hjelt Foundation for Spina Bifida in memory of Madeleine Hjelt
provided financial support for the conduct of the study and preparation
of the manuscript. The funding source had no involvement in study
design, data collection, analysis and interpretation of data, in the
writing of the report nor in the decision to submit this article for
publication.