Introduction To screen for gestational diabetes mellitus (GDM) NICE recommends a 75g oral glucose tolerance test (OGTT) at 24-28 weeks gestation only for non-diabetic women with specific risk factors. This excludes women who develop pregnancy complications associated with diabetes, such as glycosuria, large for gestational age (LGA) fetuses or polyhydramnios. Our department chose to include these in our screening criteria, and we assessed whether this alteration to the guidelines is justified.

Method Indication for screening and result was compared for all OGTTs between November 2010 and October 2011 (n=1242) in our district general maternity department. Diagnostic threshold for GDM was fasting glucose ≥5.1mmol/L and 2 hours post glucose challenge ≥7.8mmol/L. Gestation at diagnosis was recorded from notes review of 106 patients with GDM.

Results There were 195 positive results (15.7%). 15.5% of OGTTs performed for indications specified by NICE yielded positive results. The positive predictive values of 2 episodes of gestational glycosuria, a LGA fetus and current polyhydramnios were 20.8%, 16.4% and 10.1% respectively.

The median gestation at diagnosis for the indications recommended by NICE was 28 weeks. The median gestation at diagnosis for pregnancies with polyhydramnios, 2 episodes of glycosuria and a LGA fetus were 29 (IQR28-29), 30 (IQR28-33), and 36 weeks (IQR34-36) respectively.

Discussion In our population clinical signs associated with GDM compared favourably with NICE indications for screening, and can yield results early enough in gestation to allow intervention. We suggest it is inappropriate to fail to offer OGTT in light of clinical signs associated with GDM.