Patterns of Aortic Dilation in Tetralogy of Fallot: An Analysis of 100 Fetal Echocardiograms Compared With Matched Controls

Background Although aortic dilation is common in tetralogy of Fallot (TOF), its progression and risk of dissection are not well understood. The mechanism of dilation is primarily attributed to increased flow in utero; an alternative is unequal septation of the truncus arteriosus resulting in a larger aorta and inherently hypoplastic pulmonary artery (PA). If the latter is true, we hypothesize the aorta to PA ratio in TOF is stable throughout gestation, and sums of great artery dimensions are similar to controls. Methods and Results We performed a single‐center retrospective study of fetuses with TOF (2014–2020) and matched controls. We compared sums of diameters, circumferences, and cross‐sectional areas of the aorta and PA and evaluated the aorta to PA ratio across gestation in 2 TOF subtypes: pulmonary stenosis and atresia (TOF‐PA). There were 100 echocardiograms with TOF (36% TOF‐PA) with median gestational age of 31 weeks (interquartile range 26.5–34.4) and median maternal age of 34 years (interquartile range 30–37). There were no differences in sums of great artery dimensions between TOF‐pulmonary stenosis and controls. In TOF‐PA, sums were significantly lower than controls ( P values <0.01). The aorta to PA ratio was stable throughout gestation (Pearson's r =0.08 [95% CI, −0.12 to 0.27], −0.06 [95% CI, −0.25 to 0.14]). Conclusions The aorta in fetal TOF is large but grows proportionally throughout gestation, with sums of great artery dimensions similar to controls. TOF‐PA appears distinct from TOF‐pulmonary stenosis (with smaller sums), warranting further investigation. In conclusion, our findings suggest an intrinsic developmental mechanism contributes to aortic dilation in TOF.