Circulatory changes during gestational development of the sheep and human fetus.

Abstract

Circulatory changes during gestational development of the human fetus have been considered to be similar to those noted in studies of the lamb fetus. Blood flow measurements derived by Doppler ultrasound and magnetic resonance imaging techniques in human fetuses at various stages of gestation have been compared with those in the lamb. Combined ventricular output relative to fetal body weight does not change significantly with growth in the lamb or human. However, the proportion of cardiac output to the brain increases markedly in the human, but only slightly in the lamb fetus in the latter half of gestation. Cardiac output distribution to other organs also changes little in the lamb, but in the human, there is a marked decrease in the proportion distributed to the placenta and an increase in pulmonary flow. The developmental changes in the distribution of combined ventricular output in the human fetus may modify the responses to circulatory disturbances, such as congenital cardiovascular malformations, dependent on gestation.