Based on the concept that chronic increases in blood flow to any growing tissue depend on vascular growth, or angiogenesis, Meschia (1983) reasoned that ‘the large increase of blood flow to the uterus during pregnancy ...results primarily from the formation and growth of the placental vascular bed.’ In fact, numerous studies have indicated that angiogenesis is indeed a major component of the increase in placental blood flow throughout gestation, and establishment of functional fetal and placental circulations is one of the earliest events during embryonic/placental development (Reynolds & Redmer, 1995; Magness, 1998; Charnock-Joneset al.2004; Kaufmannet al.2004; Mayhewet al.2004; Reynoldset al. 2005a,b).