 It also is a common finding in stillbirths, although not regarded as a cause of these.Causes of pulmonary hypoplasia include a wide variety of congenital malformations and other conditions in which pulmonary hypoplasia is a complication.These include congenital diaphragmatic hernia, congenital cystic adenomatoid malformation, fetal hydronephrosis, caudal regression syndrome, mediastinal tumor, and sacrococcygeal teratoma with a large component inside the fetus.