Hydrops fetalis

Hydrops fetalis is excessive fluid into the third space in a fetus, which could be due to heart failure, volume overload, decreased oncotic pressure, or increased vascular permeability.

Epidemiology

The estimated incidence is ~1 in 2000 pregnancies ¹⁶ and ~1 in 1000 live births ¹⁷, although this can significantly vary according to different regions and seasons, the latter due to variance in parvovirus B19 infections ¹⁶.

Diagnosis

Hydrops fetalis is defined as the accumulation of fluid/edema in at least two of the following fetal compartments ^16,17:

• fetal pleural effusion

• fetal pericardial effusion

• fetal ascites

• skin edema (fetal anasarca)

Placental enlargement and polyhydramnios may occur secondary to hydrops fetalis but do not contribute to its diagnosis ¹⁶. Fluid accumulations in other body organs (e.g. ventriculomegaly, pulmonary cysts, dilated bowel, hydronephrosis) are not directly related to hydrops fetalis ¹⁶.

Pathology

It is considered a prenatal form of cardiac failure. It was traditionally divided into two broad groups:

• immune hydrops fetalis (IHF)

• non-immune hydrops fetalis (NIHF)

Etiology

Immune hydrops

Accounts for a minority (~10%) of cases ^8,16, although historically accounted for a larger proportion of cases in the early-to-mid 20^th century ^ref:

• fetomaternal blood group incompatibility (including rhesus incompatibility): erythroblastosis fetalis

Non-immune hydrops

Accounts for most cases (~90% ¹⁶) and can arise from a wide range causes that vary in prevalance by trimester. Chromosomal abnormalities are the most common first trimester cause ¹⁶. In the second and third trimesters, chromsomal metabolic, cardiac, and infective causes are all about equally common ¹⁶. The cause is unknown is ~20% of cases ¹⁶.

• chromosomal anomalies

  • Turner syndrome

  • trisomies

    • trisomy 13

    • trisomy 18

    • trisomy 21

• 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

• fetal tumors capable of producing significant AV shunts ³

  • sacrococcygeal teratoma

  • hepatic hemangioendothelioma

  • placental chorioangioma

• inborn errors of metabolism

  • Gaucher disease

  • Niemann-Pick disease

• fetal hypoproteinemic states

  • congenital nephrotic syndrome

• 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

• fetal skeletal dysplasia(s) ¹⁰

• fetal lymphovascular anomalies

  • cystic hygroma ⁸

• 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

  • primary fetal hydrothorax

  • congenital pulmonary airways malformation ¹¹

  • congenital diaphragmatic herniation ¹¹

  • pulmonary sequestration ¹⁴

Radiographic features

Ultrasound

Sonographic features can be similar for both immune and non-immune hydrops and include:

• increased amniotic fluid volumes (i.e. polyhydramnios)

• increased nuchal translucency (especially 1^st trimester ⁵)

• presence of a fetal pleural or pericardial effusion

• presence of fetal anemia ¹⁶

• generalized fetal body swelling: fetal anasarca and skin thickening

• placentomegaly ¹⁶ / increased placental thickness (placental edema)

• umbilical venous dilatation

Treatment and prognosis

Hydrops fetalis has a perinatal mortality rate of ~60% ¹⁶.

In the first trimester, ~67% of pregnancies end in miscarriage or fetal death in utero (FDIU) ¹⁶. Continuing pregnancy or termination or pregnancy depends on patient choice, results of any diagnostic testing, and specialist opinion ¹⁶.

In the second trimester, ~50% of pregnancies end in FDIU, and in those pregnancies that progress to live birth there is a 20% neonatal mortality rate ¹⁶.

In pregnancies after 25 weeks (including third trimester), ~15% of pregnancies end in FDIU, and in those pregnancies that progress to live birth there is a 25% neonatal mortality rate ¹⁶.

Complications

• polyhydramnios ¹⁶

• preterm birth ¹⁶

• maternal mirror syndrome (rare): pre-eclampsia like presentation with physical manisfestations of hydrops fetalis ¹⁶

History and etymology

The term hydrops fetalis comes from the Latin meaning edema of the fetus ⁶.