Hydrops Fetalis Health Article

Definition

Refers to the abnormal accumulation of fluid in the skin, body cavities, umbilical cord, and placenta of an unborn baby. Hydrops fetalis (HF) can result from many different diseases and structural defects. HF is traditionally divided into two major categories: immune HF and nonimmune HF. Immune hydrops fetalis is caused by Rh incompatibility, and was the most common cause of HF until the advent of anti-Rh antibody treatment (Rho-GAM®) during pregnancy. All other causes of HF are termed nonimmune HF. Nonimmune hydrops fetalis may be caused by chromosomal aberrations, other genetic disorders, infections, anemias, structural birth defects such as congenital heart disease, and many other conditions. Currently in the United States nonimmune HF consists of about 90% and immune HF consists of about 10% of cases.

Description

HF occurs when a baby has a condition or birth defect that causes accumulation of excess fluid, known as edema, in the skin and other body cavities. Immune HF occurs when a mother's blood group is Rh negative (this means that she does not have the Rh protein on the surface of her blood cells) and her baby's blood group is Rh positive (the baby has the Rh protein on its blood cells). During the pregnancy a small amount of the baby's blood crosses into the mother's circulatory system. When this happens, the mother's immune system recognizes the Rh protein on the baby's blood cells as foreign and makes antibodies to the Rh protein. The antibodies can then cross back over to the baby and attack its blood cells, destroying them and causing anemia. The anemia causes heart failure, subsequent edema, and, ultimately, HF. The mother's immune response becomes greater with each subsequent pregnancy in which the baby has Rh-positive blood and thus the HF becomes worse. Administration of anti-Rh antibodies during all of an Rh-negative mother's pregnancies will prevent her from ever developing an immune response to Rh-positive blood and thus will prevent HF.

The most common causes of nonimmune HF include heart disease (congenital malformations and arrhythmia), chromosome aberrations (Turner syndrome and Down syndrome), and anemia (alpha-thalassemia, fetomaternal transfusion, and twin-twin transfusion). Other causes include infections, metabolic disorders, and tumors. In all there are over 100 separate causes of nonimmune HF.

All disorders that cause HF do so by three common mechanisms that include heart failure, hypoproteinemia (low levels of protein in the blood stream), and vascular or lymphatic obstruction. Some disorders combine two or more of these mechanisms to cause HF. Most disorders cause some degree of heart failure. Anemia causes heart failure by increasing the work of the heart so much that it fails (this is termed high output heart failure). Isolated congenital heart disease or conditions that have congenital heart disease as a feature often will develop heart failure due to a poorly functioning heart (this is termed low output heart failure). Conditions that block the flow of blood or lymph can cause edema and HF. Examples include tumors and congenital malformations of the blood and lymphatic vessels. Conditions that lower that amount of protein in the blood can cause edema and HF by allowing fluid to easily leak out of the vessels and collect in the soft tissues and body cavities. Examples include metabolic conditions that damage the liver and prevent it from producing enough protein such as Gaucher disease and Sly disease.