Heart disease is the leading cause of infant death related to birth defects. Congenital heart disease in which the left sided structures of the heart (left heart hypoplasia or LHH) are too small are among the most severe, and have some of the highest death and other complication rates.

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.

Inclusion Criteria:

• Group A, C: Fetuses with hypoplastic left sided structures or at risk of coarctation of the aorta and ALL of the following

  • Any mitral annulus, aortic annulus, left ventricular end-diastolic dimension, or aortic diameter z-score less than or equal to 3.0
  • Right-left ventricular size discrepancy with no other explanation of discrepancy
  • Retrograde blood flow in the aortic arch from the ductus arteriosus
  • Left to right flow across the foramen ovale

• Group B: Healthy Fetal controls

  • Mothers undergoing screening fetal echo for family history of CHD with a normal echo.
  • Mothers undergoing fetal echocardiography for suspected heart disease with a normal echo
  • Mothers evaluated in the fetal center with normal ultrasound

• Group D:

Fetuses with hypoplastic left sided structures or at risk of coarctation of the aorta and any of the following

• Any mitral annulus, aortic annulus, left ventricular end-diastolic dimension, or aortic diameter z-score less than or equal to 2.0
• Right-left ventricular size discrepancy with no other explanation of discrepancy
• Continuous Doppler flow in the aortic arch concerning for coarctation
• Significantly less aortic flow than pulmonary artery flow
• Severe atrial septal aneurysm with possible obstruction of mitral valve flow
• Left superior vena cava to coronary sinus with dilated coronary sinus.
• Retrograde blood flow in the aortic arch from the ductus arteriosus
• Hypoplastic left heart syndrome (HLHS) and variants of HLHS
• Total anomalous pulmonary venous return

Exclusion criteria:

• Multiple gestations
• Persistent arrhythmia
• Very poor ultrasound images, defined by the inability to reliably measure/evaluate all included cardiac structures (valve annuli, branch pulmonary arteries, PFO, and arch)
• Major extra cardiac anomalies
• Aneuploidy
• Maternal conditions that may alter fetal hemodynamics, including moderate to severe HTN requiring medication in pregnancy, preeclampsia, major or unrepaired maternal congenital heart disease, obstructive sleep apnea, severe asthma (non-responsive to inhaled steroid therapy), restrictive lung disease, severe anemia, maternal chronic renal disease known placentation abnormality (complete placenta previa, accrete, or percreta), and antiphospholipid ab syndrome