Population-Level Outcomes with a 2-Step Approach for Gestational Diabetes Screening and Diagnosis

To examine outcomes associated with alternative glucose thresholds in a 2-step approach for screening and diagnosing gestational diabetes mellitus (GDM).

We studied 178,527 pregnancies between 2008 and 2012 in Alberta, Canada. They were categorized retrospectively as normal 50 g screen (n=144,191); normal 75 g oral glucose tolerance test (OGTT) (n=21,248); abnormal at glucose thresholds suggested by the International Association of Diabetes and Pregnancy Group (IADPSG) (HAPO 1.75, n=4308); abnormal at glucose thresholds associated with an odds ratio of 2.0 for adverse events in the Hyperglycemia and Adverse Pregnancy Outcomes (HAPO) study. This latter group, which would have been treated for GDM based on customary care, was further divided into those with 1 (HAPO 2-1 n=5528) or 2 or more abnormal glucose values (HAPO 2-2 n=3252). Main outcomes were large for gestational age (LGA), induced labour and Cesarean-section rates.

LGA rates were 8.2%, 10.5%, 14.2%, 11.8% and 16.5% among normal 50 g, normal 75 g OGTT, HAPO 1.75, HAPO 2-1, and HAPO 2-2 groups, respectively. Labour induction and caesarean-section rates were 29.6% and 36.2% in the IADPSG, 38.2% and 36.8% in the HAPO 2-1 group, and 42.3% and 41.1% in the HAPO 2-2 groups, respectively. Excessive maternal weight (≥91 kg) was associated with a higher risk for all adverse outcomes.

The 2-step approach effectively identifies pregnancies at low risk for adverse outcomes. Labelling influences induction practice. Any glucose intolerance increases risk for adverse outcomes, and pregnancies with highest (2 or higher) abnormal glucose values remain at greatest risk. Further research is needed to determine whether glycemic thresholds for GDM diagnosis should incorporate information about maternal weight.