Figure 1: Fetal echocardiogram before maternal oxygen therapy. (a) Color Doppler demonstrating severe tricuspid valve regurgitation (TR, annotated by the white arrow). RA: Right atrium, RV: Right ventricle, (b) Spectral Doppler noting continuous pulmonary regurgitation. (c) Color Doppler of reverse flow (left-to-right) in the patent ductus arteriosus (PDA). Ao: Aorta