Maternal undernutrition around the time of conception is associated with increased risk of insulin resistance in adulthood. We hypothesised that maternal undernutrition during the periconceptional (PCUN: -60-7d) and/or preimplantation (PIUN: 0-7d) periods would result in a decrease in UCP1 expression and the abundance of insulin signalling molecules and increased abundance of factors which regulate adipogenesis and lipogenesis in fetal perirenal adipose tissue (PAT) and that these effects would be different in singletons and twins. Maternal PCUN and PIUN resulted in a decrease in UCP1 expression in PAT and PIUN resulted in higher circulating insulin concentrations, an increased abundance of pPKC and PDK4 and a decreased abundance of Akt1, phosphorylated mTOR and PPAR in PAT in singleton and twin fetuses. In singletons there was also a decrease in the abundance of p110β in PAT in the PCUN and PIUN groups and an increase in total AMPKα in PAT in the PIUN group. In twins, however, there was an increase in the abundance of mTOR in the PCUN group and an increase in PDK2 and decrease in total AMPK α in the PIUN group. Thus exposure to periconceptional undernutrition programs changes in the thermogenic capacity and the insulin and fatty acid oxidation signalling pathway in visceral fat, and these effects are different in singletons and twins. These findings are important as the thermogenic capacity of brown fat and the insulin sensitivity of visceral fat are important determinants of the risk of developing obesity and an insulin resistance phenotype in later life.