Statistical analysis
Normally distributed continuous variables are presented as mean (±
standard deviation) and variables not following normal distribution as
median (25th - 75th percentile).
Nominal variables are summarized as counts and absolute percentages.
Distribution of continuous variables was graphically assessed by
histograms and quantile-quantile plots. Cardiac measurements were
compared between GDM and controls with the independent samples Student’s
T Test or the Mann-Whitney U Test and the chi-squared test for
continuous and categorical variables, respectively. General linear
regression models were used to assess the association between GDM and a
range of echocardiographic parameters.
To facilitate the comparison of changes in echocardiographic parameters
before and after pregnancy for the two groups of interest, we used
linear mixed models with two random effects (random intercept and random
slope) and an unstructured variance-covariance matrix. Cardiac
parameters which were used as outcome variables included E/A, E/E’,
global longitudinal strain, and myocardial performance index. An
interaction term (GDM yes/no*time interval between prenatal and
postnatal assessment) was introduced in linear mixed models to evaluate
the potential differential effect of GDM on changes in cardiac
measurements before and after delivery. Analysis was further adjusted
for a pre-specified set of confounders, including maternal age, race,
time elapsed from delivery to postnatal visit and change in infant
weight from birthweight. Statistical analysis was conducted with STATA
package, version 13.1 (StataCorp, College Station, Texas USA). We deemed
statistical significance at p <0.05. All tests were 2-tailed.