Hydrops fetalis

Last revised by Henry Knipe on 28 May 2024

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.

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.

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

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.

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)

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

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.

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

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.

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

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