Maternal Hyperoxygenation in Fetal Left Heart Hypoplasia

We intend to study a new, non-invasive fetal intervention to help outcomes in children with LHH. We plan to study the effect of giving oxygen to mothers who have fetuses with small left-sided structures. We specifically will evaluate if the fetal left heart valves will grow faster if the mother breathes extra oxygen on a daily basis (at least 8 hours per day). Mothers and fetuses meeting criteria will be offered to enroll in the study. All enrolled mothers will be asked to receive oxygen continuously for the rest of the pregnancy using a non-rebreather mask. At birth, we will compare the fetuses whose mothers received oxygen to historical controls. We specifically will study how fast the left heart valves have grown.