ABSTRACT: An association between insulin-dependent diabetes mellitus and thyroid autoimmunity has long been recognized. However, studies exploring the association of thyroid dysfunction among GDM mothers and its perinatal complications are sparse in this part of the country. Hence this study was conducted among 88 pregnant women who delivered in a tertiary care centre to determine the prevalence of thyroid disorder among the pregnant women with GDM and the fetal and maternal complications due to the thyroid disorder in GDM. Data was analysed using SPSS V21 for Windows. This hospital based retrospective study was conducted among 88 patients through the case records satisfying the inclusion and exclusion criteria to estimate the prevalence of hypo/hyperthyroidism in patients with gestational diabetes mellitus and to determine the perinatal outcome in gestational diabetes mellitus with hypo/ hyperthyroidism. Our study concludes that the prevalence of hypo/hyperthyroidism among the pregnant women with GDM was 20.5% (95% CI: 12.9%-30.7%). There was no significant association between hypo/hyperthyroidism and caesarean delivery, pre term birth, low birth weight, congenital anomalies and NICU admission. Even in terms of APGAR score and hypoglycaemia there was no significant difference between the groups. There was only one incidence of neonatal death due to extremely low birth weight of the neonate.