Circulating Delta-like homolog 1 (DLK1) at 36 weeks is correlated with birthweight and is of placental origin

•Reduced DLK1 has been reported as a fetal stress signal from those poorly grown.•We found circulating DLK1 was reduced at 28 and 36 weeks' in those carrying a SGA infant.•Circulating DLK1 at 36 weeks' gestation correlated with birthweight centile and placental weight.•Circulating DLK1 does not correlate with ultrasound measures of placental insufficiency.•DLK1 is secreted from human placental explants, thus circulating DLK1 may be of placental origin.