An experimental surgical procedure has saved a small number of affected babies, but the outlook remains grim. In most cases, doctors do not know why a baby is born with a heart defect, though both genetic and envir-onmental factors are believed to play a role. Small, underdeveloped lungs that lack sufficient cells and airways are another common cause of death. Sometimes, one or both lungs does not develop at all or is underdeveloped for reasons that are not known. Sadly, about 70 percent of babies with under-developed lungs die, usually in the neonatal period.
Chromosomal abnormalities are a common cause of neonatal death.
In most cases, when an embryo has a chromosomal abnormality it will not survive, and the pregnancy will end in miscarriage. Sometimes, the fetus does survive until birth, only to die in the early weeks of life. Birth defects involving the brain and central nervous system are another important cause of neonatal death. One example is anencephaly, in which most of the brain and skull are absent. Affected babies may be stillborn or die in the first days of life.