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 +/- edema involving at least two fetal components, which may manifest as:
- fetal pleural effusion
- fetal pericardial effusion
- fetal ascites
- generalized body edema: fetal anasarca/nuchal edema/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:
Etiology
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 tumors: 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 anemia
- coxsackie viral infection
-
congenital viral infection(s)
- fetal tumors capable of producing significant AV shunts 3
- inborn errors of metabolism
- fetal hypoproteinemic states
- congenital/fetal anemia(s)
- hemoglobin Bart's (a.k.a. Hb Bart's hydrops fetalis syndrome) 8,13
- cause of alpha thalassemia
- relatively common cause in Southeast Asia
- hemoglobin 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 edema)
- presence of a fetal pleural or pericardial effusion
- generalized 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 edema of the fetus 6.