Screening for gestational diabetes mellitus: can we be more efficient?
In a retrospective review of 471 patients screened for gestational diabetes mellitus (GDM) in a community laboratory, we compared 50 g polycose screening test results with those of the 75 g oral glucose tolerance test (GTT). The rate of GDM diagnosis was compared using criteria promulgated by the New Zealand Society for Study of Diabetes (NZSSD), Australian Diabetes in Pregnancy Society (ADIPS) and World Health Organisation (WHO). In those with borderline screening results (7.8-8 mmol/L) the rate of GDM diagnosis using NZSSD criteria was low (2.8%) compared with higher screening test results (> or = 8.1 mmol/L), where the rate was 7.4%. Corresponding rates were 7.5% and 13.5% using ADIPS criteria and 5.6% and 12.4% using WHO criteria. The predictive value of a positive 50 g screening test is therefore low, especially for the higher New Zealand criteria. In women with borderline screening results no subject had a two-hour plasma glucose of 9.0 mmol/L or more on oral GTT. This suggests that the current screening cut-off of 7.8 mmol/L might be raised to 8.1 mmol/L, resulting in a 25% reduction in the number of glucose tolerance tests. Those with significant risk factors such as macrosomia, however, still warrant greater clinical suspicion and closer follow-up.