Prenatal diagnosis of bicuspid aortic valve is challenging. Bicuspid aortic valve is often associated with aortic dilation.

Fetuses with postnatally confirmed bicuspid aortic valve were gestational age-matched with normal controls. Complex lesions were excluded. Aortic valve and arch measurements by two blinded investigators were compared.

We identified 27 cases and 27 controls. Estimated fetal weight percentile was lower in cases than controls. Seven cases had one or more significant lesions including perimembranous ventricular septal defects (n = 2), isolated annular hypoplasia (n = 2), and/or arch hypoplasia/coarctation (n = 4). Fetuses with bicuspid aortic valves had significantly smaller median z-scores of the aortic annulus (–1.60 versus –0.53, p < 0.001) and root (–1.10 versus –0.53, p = 0.040), and larger ratios of root to annulus (1.32 versus 1.21, p < 0.001), sinotubular junction to annulus (1.07 versus 0.99, p < 0.001), ascending aorta to annulus (1.29 versus 1.18, p < 0.001), and transverse aorta to annulus (1.04 versus 0.96, p = 0.023). Leaflets were “doming” in 11 cases (41%) and 0 controls (p = 0.010), “thickened” in 10 cases (37%) and 0 controls (p = 0.002). We noted similar findings in the subgroup without significant additional cardiac defects.

The appearance of doming or thickened aortic valve leaflets on fetal echocardiogram is associated with bicuspid aortic valve. Compared to controls, fetuses with bicuspid aortic valve had smaller aortic annulus sizes (possibly related to smaller fetal size) without proportionally smaller aortic measurements, resulting in larger aortic dimension to annulus ratios. Despite inherent challenges of diagnosing bicuspid aortic valve prenatally, these findings may increase suspicion and prompt appropriate postnatal follow-up.