Fetal hydrops is the abnormal accumulation of fluid in two or more body cavities or area.

Soft tissue areas or cavities include:

• Soft tissue area (Skin) >5mm
• Lungs (Pleura)
• Abdomen (Peritoneum)
• Heart (Pericardium)

Fetal hydrops happens because there is an imbalance of fluid changes in the fetal body, when more fluid is retained than resorbed. The diagnosis is usually made by ultrasound, and oftentimes there is also polyhydramnios (too much amniotic fluid) present as well as placental thickening (>4 cm in the second and > 6cm in the third trimester).

Hydrops can happen for two major reasons:

• Immune Hydrops
• Non-Immune Hydrops

Immune Hydrops

bmed_ad_r]Immune hydrops is caused by antibodies from the mother crossing the placenta and attacking fetal red cells, usually Rh isoimmunization
or alloimmune hemolytic disease.
Therefore, the first step in identifying potential reasons for fetal hydrops is to do a blood test (Coombs test) to check whether there are antibodies in the maternal blood serum. The presence of potentially harmful antibodies increases the chance that the fetal hydrops is an immune hydrops, and that hydrops is caused by destruction of fetal red cells and fetal anemia. Today, less than 10% of all cases of fetal hydrops are caused by immune issues, and the majority of fetal hydrops cases are nonimmune hydrops

Nonimmune hydrops

The incidence of nonimmune hydrops fetalis (NIHF)  is about 1 in 1,700-3,000 pregnancies. The most common cause of nonimmune hydrops are fetal cardiac anomalies followed by fetal chromosomal anomalies.

Causes of nonimmune hydrops include:

• Fetal cardiac problems
• Fetal chromosome problems
• Fetal blood problems
• Obstruction of venous or lymphatic flow
• Twin-to-twin transfusion syndrome
• Hereditary or metabolic diseases
• Diabetes
• Infections
• Anemias
• Chylothoirax
• Medications

Recent studies show that the causes of non immune hydrops can be found about 50-60% of the time prior to birth, and 85% after birth

Preterm births and polyhydramnios ioccur often.

Management: 
Once a fetal hydrops is diagnosed, the following steps are taken to check for possible causes:

1. An antibody screen (indirect Coombs test) is done in the mother's blood to differentiate between immune and non-immune hydrops.
2. A sonography of the fetus(es) to check for anomalies
3. A sonography of the placenta, 
4. Fetal echocardiography for cardiac anomalies and fetal arrhythmia, 
5. Middle cerebral artery Doppler evaluation for anemia
6. CVS or amniocentesis for fetal karyotype and/or chromosomal microarray analysis (CMA), regardless of whether a structural fetal anomaly is identified. (

The next steps are usually guided by the findings of the above tests, the gestational week, and other tests such as non stress tests and biophysical profiles.

If the fetus is stable and in the absence of clinical deterioration or other indication for earlier intervention, delivery by 37 to 38 weeks should be considered.  

The prognosis depends on the cause of the hydrops and on the gestational age at detection.  Neonatal survival is often less than 50% and higher the earlier the hydrops is diagnosed.
Even if the baby is liveborn, neonatal mortality can be over 50% except with chylothorax which has a neonatal mortality rate below 10%.