Figure 6. Blood flow, oxygen delivery and birth weight.

Geometric and line symbols are the same as in prior figures. A, across the entire sample, variation in blood flow through the umbilical vein (the total fetal nutrient supply) accounted for 17% of the variation in birth weight (P < 0.0001), but did not attain significance within each of the 4 groups (400 m Europeans y= 3049 + 1.15x, r²= 0.06, P= 0.11; 3600 m Europeans y= 2624 + 1.68x, r²= 0.09, P= 0.08; 400 m Andean y= 3443 + 0.221x, r²= 0.00, P= 0.64; 3600 m Andean y= 2867 + 1.65x r²= 0.08, P= 0.08). However when considered by altitude alone, birth weight is more closely correlated with blood flow at high altitude (inset left, 3600 m y= 3576 + 2.32x, r²= 0.16, P < 0.001; 400 m y= 3201 + 0.78x, r²= 0.04, P= 0.05), while the slopes between ancestry groups did not differ (P= 0.11). Nonetheless, for any given level of blood flow the European babies weigh ∼230 g less than Andean infants at high altitude. B, across the entire sample, variation in umbilical oxygen delivery accounted for 12% of the variation in birth weight (P < 0.0001) but this is due largely to the high altitude subjects (inset, right). Among all high altitude subjects 17% of the variation in birth weight was accounted for by oxygen delivery (y= 2724 + 13.72x, r²= 0.17, P < 0.001), while at low altitude only 3% of the variation was explained by oxygen delivery (y= 3271 + 6.17x, P= 0.12). The slopes did not differ between ancestry groups (0.56). The data again indicate that for any given oxygen delivery, the European neonate at high altitude is smaller.