The aim of this study was to explore the inter-relationship between polycystic ovary syndrome and gestational diabetes mellitus, and demonstrate maternal and fetal outcomes. This was a case-control study in 1360 pregnant women who received a diagnosis of gestational diabetes mellitus between 24 and 28 weeks of gestational age. Among all diagnosed with gestational diabetes mellitus, 150 pregnant women had received a polycystic ovary syndrome, and 160 women who did not have polycystic ovary syndrome were designated as controls. The incidence of pregnancy-induced hypertension was 26.3% and 12% in the case and control groups, respectively. Preeclampsia was seen at an incidence of 12% and 6% in case and in control groups, respectively. The difference in neonatal hypoglycemia between the two groups was statistically significant, with an incidence of 17% and 5% in the case and in control groups, respectively. This study demonstrated that the presence of polycystic ovary syndrome along with gestational diabetes mellitus increases the risk of pregnancy induced hypertension by 2.4 fold, preeclampsia by 2 fold and neonatal hypoglycemia by 3.2 fold, compared to gestational diabetes mellitus alone.