Thus, adequate blood flow to the placenta seems to be critical for normal fetal growth. At least for those substances that are diffusion limited, such as glucose, increased abundance of specific transporters and an increase in the maternal to fetal concentration gradient also seem to be important components of increased transplacental exchange (Bell et al.1999). Nevertheless, gravid uterine and umbilical glucose uptakes, which provide for about 60% of fetal metabolic needs (Reynolds et al.1986; Bellet al.1999), are reduced approximately in proportion to the reduction in placental mass and blood flows in pregnancies compromised nutritionally or by environmental heat stress (Reynoldset al.1985; Thureen
et al.1992; Wallaceet al.2002, 2005).
al. 1986; Reynolds & Redmer, 1995).