REN and fetal growth restriction: 2004; Grigore et al. 2007). However, in sheep models of IUGR induced either by 20 days of umbilicoplacental embolization (Zohdi et al. 2007) or twinning (De Matteo et al. 2008), there were no differences in plasma renin activity or ANGII concentrations when compared to controls in either fetal or postnatal life. It is possible that differences in the timing, duration, and degree of hypoxia and thus growth restriction between these models (Morrison 2008) may explain differences in the activation of the systemic RAS.