Pulmonary-to-aorta diameter ratio in the normal and abnormal fetal heart.

In an attempt to establish the normal ratio of pulmonary artery to aorta diameters at varying gestational ages, the pulmonary artery and aorta diameters of 316 normally grown fetuses between 14 and 39 weeks' gestational age were measured. The ratios for each fetus were derived, and regression analysis was used to evaluate the relationship between gestational age and each diameter. We conclude that the diameters of the pulmonary artery and aorta are closely related to fetal age but that the ratio is independent of age (mean, 1.09; SD, 0.17). The diameters of the pulmonary artery and aorta in 21 fetuses with proved congenital heart disease were then compared with those of this normal population. The pulmonary artery/aorta ratio was abnormal in 13 of 21 fetuses with congenital heart disease. Actual measurements of the great vessels can be difficult and may be misleading, but a quick comparison of relative size by inspection is feasible.