Immune Hydrops Fetalis

Immune hydrops fetalis (IHF), a form of HF, describes the excessive accumulation of fetal fluid within the fetal extravascular compartments and body cavities due to maternal rhesus (Rh) incompatibility.

Epidemiology

The incidence of IHF has decreased greatly since the introduction of RhoD immune globulin in the 1960's and has wide regional variability. The incidence in the U.K. is estimated to be at about 1/3,000 births. IHF accounts for about 10-20% of all cases of HF.

Clinical description

IHF presents during the gestational period (50% between 18-34 weeks of gestation, 50% between 34 weeks and term) and is characterized by the accumulation of fetal fluid manifesting as pericardial effusion, pleural effusion, ascites and subcutaneous edema in the fetus. The mother might notice decreased fetal movements prior to diagnosis. Fetal tachycardia, polyhydramnios and antenatal hemorrhage are often associated with HF. Mothers may develop massive anasarca, hypertension, and proteinuria (described as mirror syndrome). Death of the fetus is due to pulmonary hypoplasia and heart failure. Surviving newborns may present with respiratory distress, pale skin, jaundice, severe edema (mostly localized to the abdomen) and enlarged liver and spleen.

Etiology

IHF occurs when the mother's immune system causes a breakdown of red blood cells in the fetus (erythroblastosis fetalis). This results in destruction of fetal red blood cells by maternal IgG antibodies that cross the placenta. In feto-maternal Rh incompatibility, the maternal blood is Rh-negative and the fetal blood is Rh-positive. Rh alloimmunisation develops if maternal IgG antibodies cross the placenta, binding to antigens present on the fetal erythrocytes and causing hemolysis. Usually anti-D, anti-E, and antibodies directed against other Rh antigens comprise the majority of involved antibodies. The majority of the cases of Rh isoimmunisation lead to a mild to moderate fetal or neonatal hemolytic disease but about 20-25% of cases result in IHF.

Diagnostic methods

Diagnosis is usually by ultrasound during the 2nd to 3rd trimester of gestation. Ultrasound can detect fluid collections but if there is limited accumulation it may not be diagnosed. Having a placenta thickness of 5 mm or more, especially with a ''ground glass'' appearance on ultrasound may also be indicative of the presence of this condition. Maternal laboratory tests such as blood typing (to see if they are Rh negative), antibody screens for TORCHES-CLAP (Toxoplasma gondii; Rubella virus; Cytomegalovirus; Herpes simplex virus; Enterovirus; Syphilis; Chickenpox virus; Lyme disease; Aids; Parvovirus B19), hemoglobin electrophoresis, and an alpha-fetoprotein (AFP) test can also aid in diagnosing IHF.

Differential diagnosis

The many disorders associated with HF are differential diagnoses such as congestive heart failure, hepatitis B, Parvovirus B19 infection, hypercalcemia, hypernatremia, hypothrombinemia, hypothyroidism and diabetes (in mother) and neonatal hemochromatosis. A few conditions mimic full-blown HF such as obstructed or mature bowel, fetal abdominal cysts and an obstructed urinary system (in the end stages).

Antenatal diagnosis

Prenatal diagnosis is by ultrasound.

Management and treatment

Rh iso-immunization can usually be prevented by giving the mother an intramuscular injection of Rho(D) immune globulin. For those who develop IHF, intrauterine treatment can involve thoraco-amniotic drainage, antiarrhythmic drugs (ex. digoxin, sotalol, propranolol) to treat arrhythmia, and blood transfusion when anemia is present. If the fetus comes to term it should be delivered at a tertiary care center where the neonate can receive oxygen supplementation, medications for the kidneys and removal of excessive fluid from around the lungs and abdomen as necessary. Exchange transfusion or phototherapy can treat neonatal jaundice.

Prognosis

In most cases, prognosis is poor with a perinatal mortality rate ranging from 55-98%, but it is influenced by numerous factors.