Angiopoietin-like protein 8 (ANGPTL8), a protein implicated in lipid and glucose homeostasis, is present only in mammals, suggesting that it is involved in processes unique to these vertebrates such as pregnancy and homeothermy. We explored the role of ANGPTL8 in maternal-fetal crosstalk and its relationship with newborn adiposity. In a longitudinal analysis of healthy pregnant women, ANGPTL8 levels decreased progressively during pregnancy although remained higher than levels in the postpartum period. In a cross-sectional observational study of women with or without gestational diabetes (GDM), and their offspring, ANGPTL8 levels were higher in venous cord blood than in maternal blood, and were significantly lower in GDM patients than in healthy women. Infants small for gestational age and with low fat mass had the highest ANGPTL8 cord blood levels. Studies in vitro revealed that ANGPTL8 was secreted by brown adipocytes and its expression was increased in experimental models of white-to-brown fat conversion. Additionally, ANGPTL8 induced the expression of markers of brown adipocytes. The high levels of ANGPTL8 found in fetal life together with its relationship with newborn adiposity and brown adipose tissue point to ANGPTL8 as a potential new player in the modulation of the thermogenic machinery during the fetal-neonatal transition.