Prevalence:

• 1 in 2,000 births.

Ultrasound diagnosis:

• Abnormal accumulation of serous fluid in at least two of the following: skin (edema) and body cavities (pericardial, pleural, or ascitic effusions).
• Placentomegaly (placental thickness >6 cm) is often present.

Etiology:

• Non-specific finding in a wide variety of fetal and maternal disorders, including hematological, chromosomal, cardiovascular, renal, pulmonary, gastrointestinal, hepatic and metabolic abnormalities, congenital infection, neoplasms, malformations of the placenta or umbilical cord and genetic syndromes.
• Classically divided into:
  • Immune: 10% of cases and it is due to maternal hemolytic antibodies.
  • Non-immune: 90% of cases and it is due to all other etiologies.

Investigations:

• In many instances, the underlying cause may be determined by maternal antibody and infection screening, fetal ultrasound scanning, including echocardiography, Doppler studies, fetal blood sampling and amniocentesis for karyotyping and array.
• Often the abnormality remains unexplained even after expert post mortem examination.

Fetal therapy:

• Fetal anemia: intrauterine blood transfusions.
• Pleural effusions or large pulmonary cyst: insertion of thoracoamniotic shunts.
• Fetal tachyarrhythmias: transplacental or direct fetal administration of antiarrhythmic drugs.
• Teratomas, chorioangiomas, pulmonary sequestration: ultrasound-guided laser coagulation of feeding vessel.
• Recipient fetus in twin-to-twin transfusion syndrome: endoscopic laser coagulation of the communicating placental vessels.

Follow up:

• Scans every 2-3 weeks to monitor the evolution of hydrops.
• There is a risk of maternal morbidity due to the ‘mirror syndrome’ (combination of fetal hydrops with generalized fluid overload and a preeclamptic state in the mother).

Delivery:

• Timing and method of delivery depend on the cause of hydrops.

Prognosis:

• Depends on the cause of hydrops.
• Progressive unexplained hydrops is often lethal before or soon after birth.

Recurrence:

• Fetal defects, infection: no increased risk of recurrence.
• Part of trisomies: 1%.
• Red blood cell isoimmunisation: high.
• Metabolic disorders: 25%.