The cause of PPHN is not known. Babies are at greater risk if they have: Breathed in their own bowel movements before birth (meconium aspiration) Lack of oxygen before or during birth Infection in their lungs or blood Abnormal development of the heart or lungs Been born to a mother with diabetes mellitus Been born large for gestational age (LGA). Gestational age is the age of the baby in the womb. LGA babies are larger than more than 90% of all other babies born at the same gestational age.