Measures
The primary outcome was impaired glucose tolerance at 1 year postpartum,
defined as a HbA1c ≥5.7%. We evaluated the number of women with HbA1c ≥
6.5%, consistent with type 2 diabetes, but did not consider type 2
diabetes as an outcome because of the small number of events. Covariate
information for potential predictors of impaired glucose tolerance at
1-year postpartum were collected using surveys at study enrollment, in
which women self-identified race-ethnicity, education history, and
insurance status, and from electronic medical records, which included
information on maternal age, weight and height, pre-pregnancy BMI,
family history of type 2 diabetes, timing of GDM diagnosis and
management, and delivery and neonatal complications. Information on
plasma glucose values at 2 days postpartum was available for all study
participants via study records.
We identified potential predictors known to be associated with
progression from GDM to impaired glucose tolerance or type 2 diabetes
postpartum based on literature review.21 Covariates
were considered for inclusion into the predictive model if they were
collected during prenatal care or within 2 days of delivery, in order to
facilitate identification of women with recent GDM who may be at high
risk for progression to impaired glucose tolerance prior to hospital
discharge for delivery. Details about all candidate predictors
considered are available in Supplemental Table S1. Potentially collinear
candidate predictors were considered (e.g. pre-pregnancy BMI and
obesity) to allow the model to select the covariate(s) with the best
predictive value.22