Changing prevalence of Gestational Diabetes Mellitus during pregnancy over more than a decade

Mohammad Yawar Yakoob Madam, I read the letter1 published in the August 2020 issue of Journal of Pakistan Medical Association with interest and have some concerns. Firstly, although the authors mention about 5000 deliveries on average per year but the burden of gestational diabetes mellitus (GDM) is not expressed in absolute numbers. That is, what is missing is when authors say 6.3% prevalence in 2005 but this percentage is in relative term so what was the exact numerator and denominator to know if GDM burden is in hundreds or thousands and if number of total deliveries per year increased over time because only average is mentioned. Secondly, the prevalence figures are not population or age adjusted. It may be possible that the prevalence may have shown a temporal trend of increase over the years because of increase in population/total deliveries or more older women visiting clinics (if age is a risk factor/confounder of GDM) rather than increased pathophysiology/greater screening/diagnosis of disease or increased obesity. Population increase and age redistribution should be separated from these factors or at least mentioned as a limitation. I believe that population increase can be somewhat adjusted in percentage i.e. per 100 deliveries but what about age? If authors can provide (according to epidemiological terminology) both standardized (usually ageand sex—adjusted) and non-standardized (crude) estimates for this descriptive frequency comparison if age group-wise data is available. Thirdly, we want to inform the authors, of our study2 at The Indus Hospital in Karachi, Pakistan where we estimated the prevalence of GDM to be in the same range during approximately January to August 2017 at 17.8% (436/2451) as in this study.