Effects of reduced uterine blood flow on fetal cardiovascular, renal, and lung function.

Uterine blood flow (UBF) was reduced for 1 h by partially occluding the maternal aorta below the renal arteries in seven pregnant ewes (gestation age 126-134 days). Fetuses became hypoxic, acidemic, and hypercapnic. They developed hypertension (P less than 0.005) and a bradycardia (P less than 0.05). During restricted UBF, fetal hematocrit (Hct) rose (P less than 0.005) and blood volume fell in five of seven fetuses. After release of constriction, fetal Hct fell, and blood volume rose by 7.5 +/- 3.26% (P less than 0.05) relative to control. During reduced UBF, lung liquid and urine flow rates fell (P less than 0.025 and P less than 0.05, respectively). After the occluder was released, Na excretion (which did not fall significantly during reduced UBF) increased (P less than 0.05), and fractional reabsorption of Na fell (P less than 0.05). Changes in fetal blood volume (FBV) were directly related to changes in maternal lower body flow (r = 0.47, P = 0.01, n = 33), and changes in fetal Hct were inversely related to maternal flow (r = -0.635, P = 0.001). Fetal urinary Na excretion per kilogram body weight was directly related to FBV per kilogram (r = 0.44, P = 0.005, n = 40), whereas fractional reabsorption of Na was inversely related to FBV per kilogram body wt (r = 0.48, P less than 0.002, n = 39). It is concluded that reductions in UBF cause fetal hypoxemia and acidemia, which lead to changes in fetal cardiovascular function and in FBV.(ABSTRACT TRUNCATED AT 250 WORDS)