Physiologic impact of maternal hyperoxygenation (MH) in late gestation human fetuses with and without congenital heart disease (CHD). At baseline, the umbilical venous (UV) T2 (a) was lower in CHD fetuses than in normals. Although the UV T2 did not change significantly with MH in normals (b), we observed a significant increase in UV T2 in CHD fetuses with MH (p=0.01) (c). Both groups showed a statistically significant increase in pulmonary blood flow (PBF) during MH (d), which was more dramatic in fetuses with CHD (p=0.005) (e, f). While there was a significant reduction in ductus arteriosus (DA) flow in CHD fetuses during MH (p=0.04) (g,i), this was not present in normal fetuses (h). p ≤ 0.05 statistically significant.