The normal diameter of the fetal aorta and pulmonary artery: echocardiographic evaluation in utero.

Measurements of the fetal aorta and pulmonary artery can aid in the detection and diagnosis of congenital heart defects. In a prospective study of 403 normal fetuses whose gestational ages were between 14 and 42 weeks, two-dimensional (2D) real-time and M-mode echocardiography were used to measure the diameters of the aortic root and the pulmonary artery in utero. The goals were to establish norms for the diameters of these structures as a function of both gestational age and biparietal diameter, to compare measurements obtained in systole and diastole, and to compare 2D and M-mode measurements. A high correlation was found between measurements made during systole and diastole (r = .994 for aorta, r = .996 for pulmonary artery) and between 2D and M-mode measurements for each vessel (r = .992 for aorta, r = .973 for pulmonary artery). The differences between systolic and diastolic measurements and between M-mode and 2D measurements were small (2.2-4.6%) for both the aorta and the pulmonary artery. The norms established here provide an objective standard for comparison when a cardiac anomaly involving a fetal aorta or pulmonary artery of abnormal size is suspected. The results indicate that a sonographic facility need not have M-mode equipment to obtain technically adequate measurements.