Background: A recent study indicated an average of 19.5% abnormal oral glucose tolerance in antenatal clients per year. Aim: The purpose of this study was to determine the impact on gestational diabetes cases due to new guidelines for diagnosis and classification of hyperglycaemia in pregnancy. Materials and Methods: This study reviewed the archived clinical pathology data on oral glucose tolerance tests performed between January 1999 and December 2008 on antenatal clients (N = 615). The cases were reviewed to determine changes if any in percentage of gestational diabetes due to new guidelines. Results: Over the 10 years period, a yearly average of additional 10.8% antenatal cases suggestive of gestational diabetes was observed due to the new recommended thresholds. Further, the average yearly incidence would have increased from 8.8 cases to 16.2 cases, which translates to almost 46% increase in the prospective numbers of gestational diabetes. Conclusions: This report presents the extent of how the new recommended guidelines for diagnosis and classification of hyperglycaemia in pregnancy could increase the prevalence of gestational diabetes. It also provides pathology-based evidence for the epidemiology of gestational diabetes mellitus and allows for planning the costs that would be attendant to the full implementation of the new guidelines.