Which finding would most strongly suggest coarctation of the aorta on prenatal imaging?

• A. Diminished development of the aortic arch isthmus and altered Doppler flow in the aortic arch or ductal-dependent systemic circulation
• B. Normal arch development
• C. Increased flow in the ductus arteriosus
• D. Large arch isthmus

Answer: (C)

In fetal imaging, coarctation of the aorta is suggested when the systemic circulation becomes ductal dependent. A constriction distal to the left subclavian can limit blood flow to the descending aorta, so the fetus relies more on the ductus arteriosus to perfuse the lower body. On Doppler, this often manifests as increased flow through the ductus arteriosus, reflecting its critical role in maintaining systemic circulation. While reduced development of the aortic arch isthmus can be seen with coarctation, the strongest prenatal clue is brisk ductal flow indicating ductal-dependent systemic perfusion. Normal arch development argues against coarctation, and a large arch isthmus would be atypical for this condition.