AbstractObjective:To identify the association of the glucokinase gene (GCK) rs4607517 polymorphism with gestational diabetes mellitus (GDM) and determine whether sweets consumption could interact with the polymorphism on GDM in Chinese women.Design:We conducted a case–control study at a hospital including 1015 participants (562 GDM cases and 453 controls). We collected the data of pre-pregnancy BMI, sweets consumption and performed genotyping of the GCK rs4607517 polymorphism. Logistic regression was performed to test the association between the rs4607517 polymorphism and GDM, and the stratified analyses by sweets consumption were conducted, using an additive genetic model.Setting:A case–control study of women at a hospital in Beijing, China.ParticipantsOne thousand and fifteen Chinese women.Results:The GCK rs4607517 A allele was significantly associated with GDM (OR 1·35, 95 % CI 1·03, 1·77; P = 0·028). Furthermore, stratified analyses showed that the A allele increased the risk of GDM only in women who had a habitual consumption of sweet foods (sweets consumption ≥ once per week) (OR 1·61, 95 % CI 1·17, 2·21; P = 0·003). Significant interaction on GDM was found between the rs4607517 A allele and sweets consumption (P = 0·004).Conclusions:This study for the first time reported the interaction between the GCK rs4607517 polymorphism and sweets consumption on GDM. The results provided novel evidence for risk assessment and personalised prevention of GDM.