LAUSR

To the Editor:We read with interest the article by Koning et al [1]. The authors report that the additional women diagnosed with gestational diabetes mellitus (GDM) by the WHO 2013 definition (i.e. fasting plasma glucose [FPG] ≥5.1 mmol/l but ≤6.9 mmol/l) were more likely to be obese and have higher BMI and hypertension compared with women with normal glucose tolerance (NGT). They also report, based on unadjusted analysis using χ test and Fisher’s exact tests, that the additional group of women diagnosed by the WHO 2013 FPG criteria (WHO 2013 only fasting glucose: GDM according to new WHO 2013 fasting glucose threshold, but do not meet WHO 1999 criteria) had higher rates of planned Caesarean section and induced labour despite similar unadjusted birthweight, macrosomia and large for gestational age (LGA) rates to the NGT group. The ‘WHO 1999 only 2HG’ group (GDM according to WHO 1999 2HG threshold, but do not meet WHO 2013 criteria), who received treatment for GDM had similar rates of LGA, but lower birthweight and lower rates of macrosomia than the NGT group. Interestingly the NGT group had higher birthweight (unadjusted for gestational age or offspring sex) than those diagnosed as GDM by either criterion but similar LGA rates. Based on these results the authors conclude that treating women with mild fasting hyperglycaemia (FPG 5.1–6.9 mmol/l) would improve outcomes, including LGA. This study has several important limitations that would make this conclusion difficult to make. First, the authors reported differences in crude birthweight and not sexand gestational-age-adjusted birthweight z scores. The crude birthweight (Table 3 in Koning et al [1]) in the additional women diagnosed by the WHO 2013 FPG criteria (WHO 2013 only fasting glucose group) was higher than those in the WHO 1999 only 2HG group. This 143 g lower birthweight in the WHO 1999 only 2HG group was most likely due to the early induction, and hence lower gestational age, because of a diagnostic label of GDM. It is likely that these differences would be insignificant if birthweight z scores for gestational age and sex were used. While the authors discuss that one of the key reasons to recommend a change to the new WHO 2013 criteria is the higher LGA rates in WHO 2013 only FPG group compared with the general population (21% vs 11%), this was not statistically different from the NGT group. In fact, the LGA rates were similar across NGT, WHO 1999 only 2HG and WHO 2013 only fasting glucose groups. Second, this study did not account for the effect on birthweight of the significantly higher pre-pregnancy BMI and obesity rates in the WHO 2013 only fasting glucose group compared with theWHO 1999 only 2HG group. The statistical analysis was by unadjusted χ test/Fisher’s exact tests with no attempt to create a regression model to account for potential * Ponnusamy Saravanan [email protected]