Statistical analysis
The number of subjects selected for the study was based on power
calculations of GDF15 differences between NW or OB in previous studies
in nonpregnant subjects16,
17; a minimum of 8 subjects was needed
for a power of 0.95 and alpha= 0.05. Differences in ordered categorical
variables between the NW and OB groups were assessed with chi-square or
Fisher´s exact test; between-group differences for continuous variables
were assessed with a t test, and within-group comparisons for
continuous variables were assessed with a paired t test.
Associations between GDF15 and changes in glucose, insulin, HOMA-IR, or
HOMA-B were analysed with Pearson correlation within groups or linear
regression models, adjusted for gestational age and maternal BMI and age
at T1, for the whole population. The diagnostic plots for residuals were
reviewed and met assumptions of normality and homoscedasticity.
Categorical variables were expressed as number or percentage, and
continuous variables as mean ± SD. All tests were two-tailed;p < 0.05 was considered statistically significant.