1) The document discusses different classification systems for critical congenital heart disease (CHD) in fetuses and newborns that require urgent intervention within the first 24 hours of life.
2) It describes the most common types of critical CHD, including hypoplastic left heart syndrome (HLHS) with a restricted or closed atrial septum, total anomalous pulmonary venous return with obstruction, and transposition of the great arteries with a restrictive atrial septum.
3) For HLHS, certain Doppler ultrasound parameters measured late in pregnancy, such as a pulmonary vein flow velocity time integral ratio below 3, can help identify fetuses needing emergency intervention immediately after birth to improve survival rates.