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

Objective-To measure lung blood flow and flow through the foramen oval e in the normal human fetus and to assess the changes in each with ges tational age and the proportions of combined ventricular output that t he respective flows represent. Patients and design-38 normal fetuses ( gestational age 18-37 weeks) were studied prospectively with Doppler e chocardiography. Methods-Echocardiographic images and Doppler velocity signals were obtained from the ascending aorta, main pulmonary artery , and ductus arteriosus from each fetus and digitised to obtain arteri al diameters, heart rates, and velocity-time integrals. Blood flow in each artery was calculated as the product of heart rate, flow-velocity integral, and arterial cross sectional area. Blood flow through the l ung was assessed as the difference between flow in the pulmonary arter y and ductal flow; combined ventricular output as the sum of aortic an d pulmonary artery flows; and flow through the foramen ovale as the di fference between flows through the aorta and lungs. Results-Blood flow through the lungs increased exponentially with gestational age (r = 0 .89, p < 0.001), by almost fourfold over the period of gestation studi ed, and was a mean (SD) of 22% (7%) of combined ventricular output. Bl ood flow through the foramen ovale increased exponentially by threefol d (r = 0.77, p < 0.001), representing between 17% and 31% of combined ventricular output. Conclusions-Blood flow through the lungs and acros s the foramen ovale can be calculated non-invasively in the normal hum an fetus. Both flows increase exponentially with age and comprise betw een one fifth and one quarter of the combined ventricular output, prop ortions that remain unchanged through the second and third trimesters of pregnancy.