Hydrops fetalis is excessive extravasation of fluid into the third space in a fetus which could be due to heart failure, volume overload, decreased oncotic pressure, or increased vascular permeability. Hydrops is defined as the accumulation of fluid +/- oedema involving at least two fetal components, which may manifest as:
- fetal pleural effusion
- fetal pericardial effusion
- fetal ascites
- generalised body oedema: fetal anasarca/nuchal oedema/cystic hygroma
- placental enlargement
- polyhydramnios
- hepatomegaly
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Epidemiology
The estimated incidence is at ~1 in 2000 births although this can significantly vary according to different regions.
Pathology
It is considered a prenatal form of cardiac failure. It was traditionally divided into two broad groups:
Aetiology
Immune hydrops
Accounts for a minority (~10%) of cases in present-day pregnancies 8, although historically accounted for a larger proportion of cases in the early to mid 20th century:
- fetomaternal blood group incompatibility (including rhesus incompatibility): erythroblastosis fetalis
Non-immune hydrops
Accounts for a majority of cases and can arise from protean causes which include:
- chromosomal anomalies
- cardiac causes
- abnormalities in fetal heart rate: e.g. fetal tachyarrhythmias
- congenital cardiac anomalies
- fetal cardiac tumours: cardiac rhabdomyoma
- twin pregnancy-related complications
- twin to twin transfusion syndrome: in the recipient twin
- twin reversed arterial perfusion sequence: in pump twin
-
in utero infection(s)
-
congenital viral infection(s)
- TORCH group
- fetal parvovirus B19 infection: considered the most common infectious cause of hydrops; the mechanism is that of anaemia
- coxsackie viral infection
-
congenital viral infection(s)
- fetal tumours capable of producing significant AV shunts 3
- inborn errors of metabolism
- fetal hypoproteinaemic states
- congenital/fetal anaemia(s)
- haemoglobin Bart's (a.k.a. Hb Bart's hydrops fetalis syndrome) 8,13
- cause of alpha thalassaemia
- relatively common cause in Southeast Asia
- haemoglobin Bart's (a.k.a. Hb Bart's hydrops fetalis syndrome) 8,13
- fetal skeletal dysplasia(s) 10
- fetal lymphovascular anomalies
- high output flow states
- vein of Galen aneurysmal malformation
- umbilical vein thrombosis in cases of umbilical vein varix
- thoracic/pulmonary abnormalities: thought to be from a fetal venous obstruction
Radiographic features
Antenatal ultrasound
Sonographic features can be similar for both immune and non-immune hydrops and include:
- increased amniotic fluid volumes
- increased nuchal translucency (especially 1st trimester 5)
- larger placental size (placentomegaly) / increased placental thickness (placental oedema)
- presence of a fetal pleural or pericardial effusion
- generalised fetal body swelling: fetal anasarca and skin thickening
- umbilical venous dilatation
Treatment and prognosis
The overall prognosis can be variable, dependent on the underlying cause.
History and etymology
The term hydrops fetalis comes from the Latin meaning oedema of the fetus 6.