Pulmonary artery/aorta ratio in simple screening for fetal outflow tract abnormalities during the second trimester

Abstract

Objectives Congenital heart disease is associated with high mortality and morbidity rates, being the most life‐threatening defect in the first month of postnatal life and accounting for approximately half of all childhood mortality from birth defects. Despite this, the prenatal detection rate for congenital outflow tract anomalies by ultrasound imaging is relatively low. The aim of this study was to establish a nomogram for the pulmonary artery/aorta (PA/AO) ratio measured in the three‐vessel view plane. This ratio was investigated as a simple screening tool for congenital cardiac outflow tract abnormalities. Methods The study was a prospective evaluation of 966 singleton fetuses at 16–24 weeks of gestation and 46 fetuses with congenital cardiac outflow tract abnormalities. The diameters of the pulmonary artery and aorta were measured in the three‐vessel view. The PA/AO ratio was calculated and a nomogram was constructed. The mean and 95% CI for the ratio were defined and the PA/AO ratios of cases with outflow tract abnormalities were plotted against the values for normal fetuses. Results The gestational age of the normal group ranged from 16 to 24 weeks, with a median of 19 weeks. The pulmonary artery diameter measured between 2.1 and 4.93 mm (mean, 3.3 mm) and the aorta measured between 2.1 and 5.2 mm (mean, 2.93 mm). The mean (SD) PA/AO ratio was 1.16 (0.18) (95% CI, 0.87–1.58; range 0.61–1.86; median, 1.14). For fetuses with outflow tract abnormalities, the median gestation was 19 weeks and 37/43 (86%) had a PA/AO ratio outside the 95% CI. Conclusions The PA/AO ratio derived from measurements in the three‐vessel view plane can be used as an initial screening tool for outflow tract anomalies and may have a sensitivity of up to 86%, with a 5% false‐positive rate. Copyright © 2007 ISUOG. Published by John Wiley & Sons, Ltd.