Diagnosing gestational diabetes

Abstract

The newly proposed criteria for diagnosing gestational diabetes will result in a gestational diabetes prevalence of 17.8%, doubling the numbers of pregnant women currently diagnosed. These new diagnostic criteria are based primarily on the levels of glucose associated with a 1.75-fold increased risk of giving birth to large-for-gestational age infants (LGA) in the Hyperglycemia Adverse Pregnancy Outcome (HAPO) study; they use a single OGTT. Thus, of 23,316 pregnancies, gestational diabetes would be diagnosed in 4,150 women rather than in 2,448 women if a twofold increased risk of LGA were used. It should be recognised that the majority of women with LGA have normal glucose levels during pregnancy by these proposed criteria and that maternal obesity is a stronger predictor of LGA. The expected benefit of a diagnosis of gestational diabetes in these 1,702 additional women would be the prevention of 140 cases of LGA, 21 cases of shoulder dystocia and 16 cases of birth injury. The reproducibility of an OGTT for diagnosing mild hyperglycaemia is poor. Given that (1) glucose is a weak predictor of LGA, (2) treating these extra numbers has a modest outcome benefit and (3) the diagnosis may be based on a single raised OGTT value, further debate should occur before resources are allocated to implementing this change.

Fig. 1

a Relationship of the OR for an infant of birthweight >90th percentile vs the BMI in categories (reference group BMI <22.6 kg/m² [4]) or maternal fasting glucose in categories from HAPO (diamonds; reference group category 1 lowest glucose [2]). a The BMI relationship is adjusted for model 1 (circles) or model 2 (triangles) (see text for details). The relationship for maternal fasting glucose categories is also shown (black diamonds). b Number of participants in each category of glucose in HAPO (white bars), with number of mothers with LGA infants (black bars). c Number of participants in each category of glucose who had LGA infants