Gestational diabetes in Victoria in 1996: incidence, risk factors and outcomes

To the Editor: Stone and colleagues must be complimented for their study of gestational diabetes mellitus (GDM) published recently in the Journal.1 Although the study was comprehensive, in that it linked two pertinent records for 99.3% of the women delivering in Victoria in 1996, their analysis was necessarily limited to the parameters recorded in those two data sets.

Stone et al do not refer to relevant recent work from Toronto, Ontario,2 and Sunshine, Victoria,3 which has already determined the maternal risk factors for GDM: increasing age, racial origin, family history of diabetes mellitus, and pre-pregnancy body mass index. Data on the latter two of these four factors were specifically noted as not available to Stone's group, but could have been mentioned as established risk factors to consider in patient management.

The findings of Stone et al regarding age are similar to those previously reported. However, the relative risk for GDM in the Sunshine cohort increased from 25 years of age (odds ratio, 1.9; 95% CI, 1.3–2.7).3 Recasting the all-Victorian data1 with "< 25 years" as the reference datum would most likely produce a similarly significant result to that found in the Sunshine study.

Again, the Victorian data on racial origin are but the Sunshine data writ large. Stone and colleagues had to choose a reference datum for this parameter, but have not avoided a problem that bedevils all such work in the "New World": there is as yet no definitive Australian reference datum available for racial origin. For example, the designation "Australian" may be used, but parents who are themselves second or third generation Australian-born may have, say, pure Maltese ancestry, giving them a high risk of GDM and thus distorting the reference datum. I have argued this case in more detail elsewhere,4 and took measures to circumvent the problem in the Sunshine study.3

Among their findings, Stone et al confirm that there is a significantly increased incidence of macrosomia in GDM-affected infants. I agree. Their work is unquestionably the definitive statement of Victoria's GDM-related macrosomia status (as at 1996), but it lacks one vital ingredient: it defines macrosomia, but does not cite the source of the data used as the study's benchmark. To enable comparisons with their work in future years, could we please have that benchmark referenced so that others may use it too?