GCK and gestational diabetes: By the time of planning of this study there were two published meta-analyses confirming association of the following variants with GDM: melatonin receptor 1B (MTNR1B), glucokinase (GCK), transcription factor 7-like 2 (TCF7L2), potassium inwardly rectifying channel, subfamily J, member 11 (KCNJ11), regulatory subunit associated protein 1-like 1 (CDKAL1), insulin-like growth factor 2 mRNA-binding protein 2 (IGF2BP2) and insulin receptor substrate 1 (IRS1) (10, 11).