Statistical analysis
The data on continuous variables with normal distribution were presented
as means and standard deviations (SD). The concentration of 25(OH)D was
described as a continuous variable and categorized following the
standard of the Committee of the IOM (sufficient: ≥50nmol/L;
insufficiency:30-49.9nmol/L; deficiency:<30nmol/L). According
to the scientific literature and biological plausibility, we selected
covariables as possible confounders of the association between vitamin
D concentrations and adverse pregnancy outcomes we studied, including
maternal age and parity, since these were hypothesized to be strongly
related to vitamin D status[17].Association
between 25(OH)D levels and adverse pregnancy outcomes was assessed by
logistic regressions including these potential confounders. Logistic
regression was also used to estimate adjusted odds ratios (OR) for
adverse pregnancy outcomes during the groups. All OR were
presented with 95% confidence intervals (CIs). SPSS (version 22.0; IBM
Corp, Armonk, NY) was used for all calculations. In addition,
Women with one or more of the adverse pregnancy outcomes were defined as
“women with adverse pregnancy outcome group”, and the others were
defined as “women without adverse pregnancy outcome group”. Figure
2 was done using Graphpad Prism Version 9.00 software. Plot the
frequency distribution of vitamin D concentrations as a statistical
graph, followed by a Gaussian fit.