Assessment of changes in blood flow through the lungs and foramen ovale in the normal human fetus with gestational age: a prospective Doppler echocardiographic study.

Abstract

Blood flow through the lungs and across the foramen ovale can be calculated non-invasively in the normal human fetus. Both flows increase exponentially with age and comprise between one fifth and one quarter of the combined ventricular output, proportions that remain unchanged through the second and third trimesters of pregnancy.