Fetal aortic stenosis is an anatomically simple birth defect in which there is partial blockage of the aortic valve, limiting blood flow out of the left side of the heart. If the blockage becomes severe in fetal life, the left heart structures may stop growing and the baby may be born with hypoplastic left heart syndrome (HLHS), a lethal condition without neonatal heart surgery or heart transplantation. Standard treatment for babies born with HLHS includes three major cardiac operations before the age of 6 years. Postnatal outcomes for HLHS are uncertain and vary with patient; however, the few adult survivors are currently suffering substantial medical problems, including a high incidence of neurologic problems. For fetuses with severe obstruction, fetal intervention may improve outcomes by increasing flow through the left heart, thus improving left heart function and encouraging continued growth of the left heart structures. If fetal intervention can preserve left heart function and growth, this should provide a better prognosis for the baby and allow for biventricular repair strategies after birth.~This research study is a prospective, non-randomized clinical trial of 30 patients that will assess the safety and efficacy of in utero percutaneous balloon dilation of fetal aortic valve with severe stenosis. This technique has been successfully used to perform postnatal aortic valve dilations for several decades, but has had limited application and study in utero.~Pregnant women carrying a fetus diagnosed with severe aortic stenosis will be referred to the University of California, San Francisco Fetal Treatment Center for evaluation, initial screening and counseling. If all fetal and maternal inclusion criteria are met, the balloon aortic valvuloplasty operation will be offered to the pregnant woman. Patients who do not meet study eligibility or decline prenatal intervention will be offered the option to enroll as a study control.
For fetuses with severe aortic stenosis, in utero balloon aortic valvuloplasty may improve fetal growth of left heart structures and thus improve potential for biventricular repair strategies after birth.