Introduction Obesity is an increasing problem. In October 2010, Countess of Chester Hospital adopted recommendations by IADPSG for diagnosis of GDM. We aimed to review the impact of the recommendations, and determine the association of booking BMI on glycaemic management and pregnancy outcomes.

Methods The number of GDM diagnosed 12 months before and after the change in criteria was compared. Data was retrospectively collected on women diagnosed with GDM using new criteria (fasting blood glucose ≥5.1mmol/l, 2 hr glucose ≥7.8mmol/l). Outcomes were compared between obese women (BMI≥30) and those with BMI<30.

Results In a mainly Caucasian population, 186 (15%) women were diagnosed with GDM (new criteria from 1228 OGTT), compared with 45 (4.1%) women diagnosed (old criteria from 1089 screened). Analysis of 82 cases (mean age 31±5.4, mean BMI 30±6.9kg/m2) diagnosed on the new criteria showed obese women had more adverse pregnancy outcomes and required more intervention with metformin (34.1% vs 23.7%) and insulin (29.5% vs 13.2%) for glycaemic control than non-obese women.

Conclusions The new recommendations have increased the diagnosis of GDM by 4 fold. Obesity may further increase the risks of perinatal morbidity associated with GDM, and the reasons for this needs further research.