ABSTRACTObjectivesTo analyze the prevalence and severity of fetal aortic regurgitation (AR) after undergoing successful fetal aortic valvuloplasty (FAV) and to evaluate its effects on fetal circulation and left ventricular (LV) growth.MethodsThis was a retrospective review of all fetuses with critical aortic stenosis who underwent successful FAV at our center between 2010 and 2024 for whom postnatal echocardiograms were available in digital format. Fetal and postnatal echocardiographic examinations were analyzed for ventricular and valvular dimensions and characteristics, and Z‐scores were calculated for middle cerebral artery (MCA) pulsatility index (PI), umbilical artery (UA) PI and cerebroplacental ratio. AR severity was classified into no/mild AR or significant (moderate/severe) AR. The balloon‐to‐aortic valve ratio (BVR) was calculated as the ratio between the maximum actual balloon diameter and the aortic valve (AV) annulus diameter. The primary endpoints of this study were the prevalence, severity and risk factors for fetal AR following successful FAV.ResultsNinety‐nine fetuses who underwent successful FAV were included. Immediate post‐FAV echocardiograms showed that 87% of fetuses developed some degree of AR, including 45% of all fetuses with significant AR. BVR was significantly higher in fetuses with significant AR compared to those with no/mild AR (mean, 1.09 (95% CI, 1.06–1.12) vs 1.02 (95% CI, 0.99–1.04); P < 0.001). In a subgroup of 66/99 fetuses with available postnatal echocardiograms, the prevalence of AR decreased significantly from 86% before birth to 58% after birth (P < 0.001), with the proportion of fetuses with significant AR reducing from 47% before birth to 17% after birth (P < 0.001). In the overall cohort of fetuses, AV maximum velocity (Vmax) increased significantly from post‐FAV to after birth (mean, 1.93 (95% CI, 1.75–2.11) m/s vs 3.21 (95% CI, 2.89–3.55) m/s; P < 0.001), regardless of AR severity, but Vmax after birth was lower in the significant‐AR group compared with the no/mild‐AR group (mean, 2.85 m/s vs 3.55 m/s; P = 0.020). Fetuses with significant AR exhibited higher relative LV length increases from immediately post‐FAV to after birth than did those with no/mild AR (25% (95% CI, 16–33%) vs 14% (95% CI, 6–21%); P = 0.044), although there was no significant difference in mean LV length Z‐score after birth between the two groups. FAV led to significant short‐term increases in MCA‐PI and UA‐PI Z‐scores, with greater increases observed in fetuses with significant AR.ConclusionsFAV is associated with a high prevalence of fetal AR, which lessens in severity over the course of gestation. Significant fetal AR had the largest association with greater BVR and had significant impact on fetal hemodynamics. © 2025 The Author(s). Ultrasound in Obstetrics & Gynecology published by John Wiley & Sons Ltd on behalf of International Society of Ultrasound in Obstetrics and Gynecology.