An altered one-carbon cycle is known to influence placental and fetal development. We hypothesize that deficiency of maternal micronutrients like folic acid and vitamin B12 will lead to increased oxidative stress, reduced long-chain polyunsaturated fatty acids and altered expression of peroxisome proliferator activated receptor (PPARγ) in the placenta and omega-3 fatty acid supplementation to a these diets will increase the expression of PPARγ. Female rats were divided into five groups: Control; Folic acid deficient (FD); Vitamin B12 deficient (BD); Folic acid deficient + omega-3 fatty acid supplemented (FDO); and Vitamin B12 deficient + omega-3 fatty acid supplemented (BDO). Dams were dissected on gestational day 20. Maternal micronutrient deficiency leads to lower (p<0.05) levels of placental docosahexaenoic acid (DHA), arachidonic acid (ARA), PPARγ expression and higher (p<0.05) levels of plasma malonidialdehyde (MDA), placental IL-6 and TNF-α. Omega-3 fatty acid supplementation to a vitamin B12 deficient diet normalized the expression of PPARγ and lowered the levels of placental TNF-α. In case of supplementation to a folic acid deficient diet it lowered the levels of MDA and placental IL-6 and TNF-α. This study has implications for fetal growth since oxidative stress; inflammation and PPARγ are known to play a key role in the placental development.