Uteroplacental blood flow during pregnancy in chronically catheterized guinea pigs.

Uterine blood flow and its distribution to uterus, placenta and subplacental structures was measured in 18 pregnant guinea pigs studied under chronic steady-state conditions. Maternal cardiac output averaged 266 +/- 14 ml/min. Placental blood flow (PBF) remained less than 4 ml/min until 50 days gestation, after which it increased rapidly, attaining flows of 16 ml/min at term. PBF also increased linearly with placental weight (r = 0.76, P less than 0.001); however, the increase in PBF with gestational age is evident even in narrow weight ranges, indicating hyperperfusion of term placentas relative to those earlier in gestation. Fetal weight correlated with measured placental blood flow supplying the corresponding placenta after 50 days gestation (r = 0.72, P less than 0.001).