LAUSR

A 28‐year‐old primigravida presented for fetal echocardiography at 13 weeks' gestation owing to nuchal translucency thickening (3.5 mm) and fetal edema. The sonography revealed right atrial and ventricular enlargement and severe tricuspid regurgitation (Figure 1A). A single arterial vessel without a definite semilunar valve straddled a large ventricular septal defect (Figure 1B, Movie S1). A stenotic vessel arising from the single artery (Figure 1C, Movie S2), and aberrant right subclavian artery (Figure 1D) were also noticed. Doppler ultrasonography revealed “to‐and‐fro” flow in the single artery (Figure 1E–G, Movie S2). Hence, the main diagnosis was type I truncus arteriosus (TA) with absent semilunar valve (ASV). The autopsy confirmed the diagnosis (Figure 2). Whole‐genome sequencing demonstrated trisomy 13 (47, XY, +13). TA accompanied by ASV is an exceedingly rare heart malformation with poor prognosis. Identification of such significant heart malformation in first trimester allows timely access to specialist counselling and genetic diagnosis.