hydrops fetalis

the accumulation of fluid in fetal tissues or body cavities. This may take the form of a cystic hygroma. In its most severe form, excessive fluid collects in the peritoneal cavity (see ascites), the pleural and pericardial cavities, and the soft tissues (see oedema). Hydrops may occur at any stage of gestation but is not usually seen until 16–18 weeks; the earlier it presents, the worse the prognosis. There are several causes of hydrops, one of which is severe anaemia associated with rhesus factor incompatibility (see haemolytic disease of the newborn). Other (nonimmune) causes include congenital heart defects, fetal arrhythmias, chromosomal abnormalities, and fetal infection with human parvovirus B19. Treatment before birth with intrauterine blood transfusions to the fetus may be undertaken in specialized fetal medicine units; without treatment the mortality is high. Prenatal ultrasound scanning enables early recognition of hydrops fetalis.