Which diagnosis should be considered in a newborn with feeding difficulties and tachypnea?

In considering a newborn with feeding difficulties and tachypnea, the most relevant diagnosis to explore is Atrial Septal Defect (ASD). ASD is a congenital heart defect characterized by an opening in the septum that divides the heart's chambers. In newborns, this condition can lead to increased blood flow to the lungs, causing respiratory symptoms such as tachypnea (rapid breathing).

The combination of feeding difficulties and tachypnea in a newborn may suggest that the infant is experiencing heart failure due to the excessive workload placed on the heart and lungs from the shunting of blood associated with ASD. Infants with cardiac issues often exhibit failure-to-thrive symptoms, which can include poor feeding or lethargy.

Other conditions listed, such as congenital hypothyroidism, cystic fibrosis, and pneumonia, have distinct clinical features that may not align as closely with both symptoms. For instance, congenital hypothyroidism typically does not present with acute feeding difficulties or tachypnea in the immediate newborn period. Cystic fibrosis is more often characterized by meconium ileus or frequent respiratory infections, and pneumonia would usually present with fever, cough, and possibly more pronounced respiratory distress. Thus, ASD stands out as a significant potential diagnosis in this scenario,