Statistical Methods
Data were expressed as mean (standard deviation) for continuous variables and n (%) for categorical variables. Students t-test and χ2-square test or Fisher’s exact test, were used for comparing outcome groups for continuous and categorical data, respectively.
Univariable logistic regression analysis was performed to examine the association between racial origin and PE and GH using white racial origin as the reference. Multiple logistic regression analysis with manual backward elimination was performed for modelling total PE, preterm PE with delivery at <37 weeks of gestation, early PE with delivery at <34 weeks and total GH using racial origin, maternal age, weight, height, mode of conception, smoking, history of chronic hypertension, diabetes mellitus, APS or SLE, history of PE in a previous pregnancy or family history of PE. Before performing the multiple regression analysis, continuous variables were centered by subtracting the median from each measured value (67 from maternal weight in kg, 1.65 from maternal height in meters and 30 from maternal age in years).
The statistical software R was used for data analyses.29