Obesity, affecting one in three pregnant women worldwide, is not only a major obstetric risk factor. The resulting low‐grade inflammation may have a long‐term impact on the offspring's HPA axis through dysregulation of maternal, placental and fetal corticosteroid metabolism, and children born of obese mothers have increased risk of diabetes and cardiovascular disease. The long‐term effects of maternal obesity on offspring neurodevelopment are, however, undetermined and could depend on the specific effects on placental and fetal cortisol metabolism. This systematic review evaluates how maternal obesity affects placental cortisol metabolism and the offspring's HPA axis. Pubmed, Embase and Scopus were searched for original studies on maternal BMI, obesity, and cortisol metabolism and transfer. Fifteen studies were included after the screening of 4556 identified records. Studies were small with heterogeneous exposures and outcomes. Two studies found that maternal obesity reduced placental HSD11β2 activity. In one study, umbilical cord blood cortisol levels were affected by maternal BMI. In three studies, an altered cortisol response was consistently seen among offspring in childhood (n = 2) or adulthood (n = 1). Maternal BMI was not associated with placental HSD11β1 or HSD11β2 mRNA expression, or placental HSD11β2 methylation. In conclusion, high maternal BMI is associated with reduced placental HSD11β2 activity and a dampened cortisol level among offspring, but the data is sparse. Further investigations are needed to clarify whether the HPA axis is affected by prenatal factors including maternal obesity and investigate if adverse effects can be ameliorated by optimising the intrauterine environment. Maternal obesity affects the offspring's cortisol metabolism differently before and after birth. Around birth, the placental enzyme HSD11β2 that catalyses active cortisol into cortisone is downregulated and the umbilical cortisol level is decreased. In childhood, the offspring's HPA axis becomes overloaded with an increased cortisol steepness which triggers a cortisol blunt in adulthood. Thus, maternal obesity might increase the risk of cognitive and affective disabilities in exposed children.