Foetal hydrops is the accumulation of fluid in two or more foetal compartments, including ascites, pleural effusion, pericardial effusion and skin oedema. In ultrasound, it often presents as increased skin thickness.
Description
Foetal hydrops is a serious foetal condition defined by abnormal accumulation of fluid in two or more foetal compartments, including pertioneal cavity, pleura, pericardium). It is usually a sign of severe systemic disease and is categorised into two types: immune and non-immune hydrops foetalis.
Pathogenesis
Immune hydrops foetalis occurs due to maternal-foetal blood group incompatibility, often involving the Rhesus (Rh) factor, leading to severe foetal anaemia. Non-immune hydrops foetalis, which now accounts for the majority of cases, has a myriad of causes, including cardiac, chromosomal and metabolic disorders, infections, and tumours.
Subtypes
- Immune hydrops foetalis: Less common type of hydrops in developed countries, due to the widespread use of Rh immunoglobulin prophylaxis. It typically results from severe foetal anaemia induced by maternal-foetal blood group incompatibility, most often involving the Rhesus (Rh) factor. The maternal immune system produces antibodies against the foetal blood cells, leading to haemolysis. The foetus tries to compensate for the anaemia by pushing the immature erythroblasts from the liver and spleen into the circulation, a condition termed erythroblastosis foetalis. The increased cardiac output due to anaemia can eventually result in heart failure and hydrops.
- Non-immune hydrops foetalis: More common type, accounting for approximately 90% of all cases. It results from a variety of diseases, such as foetal arrhythmias, structural abnormalities (like congenital cystic adenomatoid malformation of the lung, diaphragmatic hernia), chromosomal abnormalities (like Turner syndrome), infectious diseases (like parvovirus B19, CMV, syphilis, toxoplasmosis), metabolic disorders, and tumours (like sacrococcygeal teratoma). Non-immune hydrops is often more difficult to manage because the underlying conditions can be quite diverse, and some are not treatable in utero. The mechanism of fluid accumulation varies depending on the underlying disorder but can involve lymphatic obstruction, congestive heart failure, or inflammation.
Epidemiology, Risk Factors & Associations
- Non-immune hydrops is now more common than immune hydrops, largely due to Rh immunoglobulin prophylaxis (Rh(D) immune globulin).
- Non-immune hydrops can be associated with a variety of conditions, including cardiovascular (20%), chromosomal (karyotype abnormalities ~23%), and haematologic (6%) abnormalities, among others.
- Immune hydrops is almost exclusively associated with Rh incompatibility.
Clinical Features
- Often detected incidentally during routine ultrasound examinations.
- Immune hydrops: maternal serological examination shows alloimmunisation, usually anti-D.
- Non-immune hydrops: wide range of clinical presentations depending on the underlying cause.
Complications
- High risk of perinatal mortality (up to 90% in cases with unknown etiology).
- If caused by chromosomal abnormalities, long-term prognosis depends on the specific abnormality.
- Immune hydrops, if untreated, can lead to death due to severe anaemia and high-output heart failure.
Pathological Features
Histopathology
- Macroscopic: Generalised body swelling, effusions into body cavities.
- Microscopic: Generalised oedema at cellular level.
Serology
In cases of immune hydrops, positive maternal indirect Coombs test.
Biochemistry
Not directly applicable.
Radiological Features
General Features
- Characteristically demonstrates an increase in the thickness of skin (>5mm) and presence of effusion in two or more compartments: pleural, pericardial, ascites.
- Generalised increase in echogenicity of the subcutaneous tissue layer.
US
- B-mode: Visualisation of an abnormal amount of fluid in the foetal body and/or surrounding the foetus.
- Colour: Not typically relevant in this context.
Grading and Staging
There is no formal grading or staging system for foetal hydrops.
Diagnosis
Diagnosis is usually via ultrasound demonstrating fluid accumulation in two or more foetal compartments. Detailed ultrasound and possible foetal echocardiography are required to determine underlying cause.
Differential Diagnosis
- Twin-to-twin transfusion syndrome: typically in a multiple pregnancy.
- Other causes of foetal oedema, such as Noonan syndrome: characterised by distinctive facial features, short stature, and heart defects.
Management
Management is dependent on the underlying cause. In cases of immune hydrops, intrauterine blood transfusion may be considered. Most cases of non-immune hydrops will need delivery in a tertiary centre with neonatal intensive care facilities. Foetal intervention is limited to treatable causes such as arrhythmias or large arteriovenous malformations.