Most congenital lung lesions do not become visible until early in the second trimester. They often grow, sometimes fast, causing the lung on the same side to be compressed. In addition, the heart may be pushed to the other side, and even the lung on the other side may be compressed. If the lesion becomes very large, it may start to affect the well-being of the fetus. Extreme compression of the heart and the large blood vessels of the chest may impair the heart's function, and this could lead to hydrops (heart failure) and death. If compression of organs in the chest is severe and continues for a long time during pregnancy, the baby's lungs may not function well at birth (pulmonary hypoplasia).
In most cases, however, growth of these lesions is limited, and they tend to become smaller toward the end of the second trimester. In approximately 75% of the cases, the lesion regresses either partially or completely by the time the baby is born; not uncommonly, the lesion is not visible by prenatal ultrasound anymore.
Of course, premature birth can affect the outcome, particularly if it occurs as the lesion is still large and compressing the lungs. However, the presence of a congenital lung lesion does not in itself increase the risk of prematurity.
The Fetal Treatment Program is a partnership of Hasbro Children's Hospital, Women & Infants' Hospital and The Warren Alpert Medical School of Brown University.