HPRT1 and fetal growth restriction: At GD20, the comprehensive gene ranking in male rat cartilage in the PDE-induced IUGR model was RPL4, RPL5, SDHA, GAPDH, 18S, HPRT1, ACTB, GUSB (Figure 3K); at PW6, the ranking was SDHA, RPL5, RPL4, GAPDH, ACTB, 18S, GUSB, HPRT1 (Figure 3L); and at PW12, it was RPL5, ACTB, SDHA, GAPDH, 18S, HPRT1, RPL4, GUSB (Figure 3M).