Interestingly both estrogen and progesterone levels have recently been shown to be lower in the serum of IUGR pregnancies than healthy controls (77), and a recent mouse model of stress induced IUGR has also shown that pregnant dams exhibited reduced progesterone levels and placental heme oxygenase 1 (Hmox1) expression and an increase in cytotoxic CD8+ T cells (78). This evidence concerns the gene CD8A and fetal growth restriction.