Role of predelivery fetal echocardiography, cardiac magnetic resonance imaging and acute maternal hyperoxygenation in predicting urgency of neonatal balloon atrial septostomy in fetal dextro‐transposition of the great arteries

ABSTRACT Objective Newborns with dextro‐transposition of the great arteries (TGA) without adequate intracardiac shunting of oxygenated blood are at imminent risk of severe hypoxia at birth. Using fetal echocardiography and cardiac magnetic resonance imaging (CMR) in room air (RA) and during acute maternal hyperoxygenation (AMH), we sought to identify predelivery imaging features predictive of neonatal hypoxia and the need for urgent balloon atrial septostomy (BAS) within the first 3 h after birth. Methods This was a prospective single‐center cohort study of pregnancies with TGA with an intact ventricular septum (IVS) or a single ventricular septal defect (VSD) ≤ 4 mm. Fetal echocardiography and, if feasible, CMR were conducted concurrently at 34–38 weeks' gestation. Cardiac structures, including the foramen ovale (FO) and atrial septum, were examined using two‐dimensional and Doppler echocardiography. CMR was used to quantify fetal weight, brain volume and vascular oxygen saturation (SaO 2 ). Both imaging modalities were used to assess fetal vascular blood flows in RA and during AMH. Postnatal data collected included preductal oxygen saturation (SpO 2 ) and the need for and timing of BAS. Univariable logistic regression analysis was used to evaluate associations between predelivery imaging features and the need for urgent neonatal BAS. Results Of 34 newborns with TGA/IVS ( n = 29) or TGA/VSD ( n = 5), 23 (68%) underwent neonatal BAS, including 12 cases of urgent BAS < 3 h after birth for persistent preductal SpO 2 < 70%. A fetal echocardiogram was obtained in all cases, while 26/34 (76%) underwent CMR, including 9/12 (75%) cases that underwent urgent BAS. On univariable logistic regression analysis, abnormal atrial septal flap morphology in RA ( P = 0.004), effective FO size ≤ 3.4 mm during AMH ( P = 0.0024) and constricted or continuously reversed diastolic flow across the ductus arteriosus (DA) during AMH ( P = 0.0006) were the most significant predictors of urgent neonatal BAS. On CMR, fetuses with an ascending aorta (AAo)/main pulmonary artery (MPA) SaO 2 ratio > 1 during AMH were significantly more likely to undergo urgent BAS postnatally (odds ratio, 28.6 (95% CI, 1.1–620.3); P = 0.0084). Conclusion In fetuses with TGA, predelivery assessment of atrial septal morphology in RA, as well as effective FO size, DA flow pattern and AAo/MPA SaO 2 ratio > 1 during AMH, are the most useful variables for predicting the need for urgent neonatal BAS. © 2026 International Society of Ultrasound in Obstetrics and Gynecology.