During pregnancy, the adipokines leptin and adiponectin can affect placental nutrient transport and inflammatory pathways, potentially leading to altered fetal growth and pregnancy complications including gestational diabetes mellitus (GDM) and preeclampsia (PE). The aim of this systematic review is to gather and analyze research on maternal circulating leptin and adiponectin levels and their relationship to adverse pregnancy and birth outcomes. Additionally, it seeks to determine whether these hormones are linked to alterations in placental transporters and cell signaling pathways. PubMed and MEDLINE were systematically searched to include studies published between 2012 and 2022. All primary data studies reporting serum adiponectin and/or leptin, placental mRNA and protein levels of related transporters, and adverse birth outcomes were eligible. The current systematic review encompasses a total of 14 articles. Abnormal serum maternal leptin and adiponectin levels were associated with changes in fetal growth and placental cellular signaling and nutrient transporters. A majority of studies associated elevated maternal leptin and reduced adiponectin with fetal overgrowth, although this relationship was not consistent and may be complicated when other pathologies are present. The effects of maternal leptin and adiponectin on fetal growth may be driven by placental adaptation in nutrient transporters and mitochondria. Future studies should determine if the placental effects of leptin and adiponectin that have been found in models have mechanistic roles in human pregnancy.