Hydrops fetalis is characterized by the abnormal accumulation of fluid collections or edema in at least two fetal compartments.
In utero, signs of hydrops fetalis include larger than normal uterine size for dates and decreased fetal movement. Although many times there are no signs or symptoms and a fetus is discovered to have hydrops fetalis during a routine ultrasound exam.
Prenatal diagnosis is established by ultrasound examination. The following conditions, which are indicative of hydrops fetalis, may be seen on ultrasound:
- Ascites – Fluid in the intra-abdominal organs (liver, bladder).
- Pleural effusions – In the chest, pleural effusions may be seen outlining the lungs, just inside the chest wall. Long standing effusions developing prior to 20 weeks of gestation may hamper the grown and development of the lung tissue, which can lead to pulmonary hypoplasia.
- Pericardial effusion – Pericardial effusions can be measured using M-mode ultrasonography.
- Skin edema – The presence of skin edema is a late sign of fetal hydrops. Pathologic skin edema appears as subcutaneous tissue thickness on the chest or scalp greater than 5mm.
- Polyhydraminos – Polyhydraminos is defined as amniotic fluid index greater than 24 cm or a maximum vertical pocket greater than 8 cm. It is present in 40% to 75% of pregnancies complicated by hydrops fetalis .
- Placentomegaly – The placenta may be larger than normal due to intravillous edema. A placental thickness of greater than 5 cm is considered abnormal and should be further evaluated  .
Management consists of a search of the etiology of hydrops since treatment of the underlying condition may allow treatment and prevent recurrence with future pregnancies.
Evaluation consists of:
- Obtaining a patient and family history to evaluate for heritable disorders associated with hydrops such as thalassemia, metabolic disorders and genetic syndrome; inquiry about recent exposure to infectious agents – parvovirus B 19 is the most common etiology of hydrops, accounting for almost 15% of cases.
- An ultrasound exam to look for major fetal structural abnormalities should be performed.
- Laboratory tests can also be performed on the mother: complete blood count, serology to evaluate for viral infections such as CMV, parvovirus, toxoplasmosis.
- Laboratory tests can be performed on the fetus: fetal karyotype and genetic microarray molecular testing can be done using amniocenteses or fetal blood sampling.
Treatment depends on the etiology and symptoms at birth. For example, oxygen or mechanical breathing support may be provided at birth to a fetus with difficult breathing, removal of excessive fluid from the pleural space and abdomen may be performed at the time of birth, medications may be administered to help the fetus’s kidneys remove the excess fluid.
Hydrops is a poor prognostic indicator for perinatal survival. Prognosis depends upon the etiology, the gestational age at onset and whether pleural effusions are present. In general, the earlier hydrops occurs, the worse the prognosis. Maternal-fetal medicine specialists and neonatologist should be involved in the management of any pregnancy with a diagnosis of hydrops fetalis.
Careful surveillance of maternal status is key because of increased risk of preeclampsia, dystocia during labor and postpartum hemorrhage. Delivery should be performed at a medical center with a neonatal intensive care unit.
The etiology remains unclear. Some of the known causes of hydrops fetalis include:
- Hematologic problems such as fetal hemorrhage
- Disorders of red blood cell production
- Genetic hemolytic disorders
- Congenital infections such as syphilis, cytomegalovirus (CMV), parvovirus
- Genetic abnormalities or syndromes
- Tumors such as diaphragmatic hernia, sacrococcygeal teratomas, polycystic kidneys
- Cardiovascular abnormalities attributed to structural problems of the heart, arrhythmias, vessel abnormalities
The incidence of non-immune hydrops fetalis ranges from 1/1500 to 1/3800 births    . Non-immune hydrops fetalis is associated with an overall perinatal mortality rate of 50 to 98%.
In the fetus, cellular mechanisms including the presence of membrane proteins such as aquaporin and the extracellular glycocalyx within the membrane serve to regulate fluid movement. A dysregulation of these mechanisms and/or proteins results in abnormal fluid movement causing hydrops fetalis.
The abnormal fluid movement can be a result of: obstructed lymph drainage in the thoracic and abdominal cavities, increased capillary permeability resulting in infection, increased venous pressure due to heart failure or obstructed venous blood return to the heart, reduction in osmotic pressure resulting in liver disease, nephropathy or non-immune mediated anemia, and/or abnormal levels of aldosterone and atrial natriuretic factor  .
There is no guideline for the prevention of hydrops fetalis.
Hydrops fetalis refers to the abnormal accumulation of fluid collections in at least two compartments, in the fetus: ascites (abdominal cavity), pleural effusion (lining of lungs), pericardial effusion (around the heart), skin edema (anasarca), polyhydraminos (excess amniotic fluid).
There are two types of hydrops fetalis: immune and non-immune. Immune hydrops (erythroblastosis fetalis) occurs when the maternal immune system attacks the fetal blood cells. Immune hydrops fetalis is no longer present in many developed countries due to the use of RhoGAM iummoglobulin (Ig) prophylaxis given in at-risk mothers.
Non-immune hydrops fetalis results when a disease or other complication interferes with the fetus’s ability to regulate fluid.
Hydrops fetalis occurs when large amounts of fluid builds up in a baby’s tissues, while it is inside the mother. The fluid results in swelling and other problems in the fetus. There are two kinds of hydrops fetalis: immune and non-immune. Immune hydrops fetalis occurs when cells in the mother’s immune system attacks the baby’s cells. This type of hydrops fetalis is no longer common in developed countries due to the invention of Rhogam. Non-immune hydrops fetalis occurs for unknown reasons, possibly due to an infection or other fetal abnormality.
What are the symptoms?
Often times, there are no symptoms and a fetus is discovered to have hydrops fetalis when a routine ultrasound is performed. Other times, the mother starts to experience problems during her pregnancy such as preeclampsia. Hydrops fetalis may be diagnosed after the birth of the baby, if the baby has difficulty breathing or other problems at the time of birth.
How is it diagnosed?
Diagnosis can be made during pregnancy or after the baby is born through: ultrasound, fetal blood sampling or amniocentesis.
What is the treatment?
Hydrops fetalis can be life-threatening. The treatment depends on the cause of the fluid build-up. For example, oxygen or mechanical breathing support may be provided at birth to a fetus with difficult breathing, removal of excessive fluid from the pleural space and abdomen may be performed at the time of birth, medications may be administered to help the fetus’s kidneys remove the excess fluid.
Maternal-fetal medicine specialists and neonatologist should be involved in the management of any pregnancy with a diagnosis of hydrops fetalis. Delivery should be performed at a medical center with a neonatal intensive care unit.
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