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Blood | Fetal hydrops

Fetal hydrops, also known as hydrops fetalis, is a serious condition defined by the accumulation of abnormal fluid in at least two different fetal compartments. It implies an excess of total body water either under the skin, around the lungs or heart, or in the abdomen. It may also be associated with an excess of amniotic fluid (polyhydramnios) or a thickened placenta. Fetal hydrops can be life-threatening for the fetus.

Essential Information

  • In fetal hydrops, excess water accumulates either under the skin (subcutaneous edema), around the lungs or heart (pleural or pericardial effusions), or in the abdomen (ascites).
  • Fetal hydrops is usually associated with a poor prognosis. It may result in miscarriage, especially if it develops in early pregnancy. Some causes are amenable to in-utero
  • Mothers of hydropic fetuses are at risk of developing a “mirror” syndrome, whereby generalized maternal swelling (edema) develops that ‘mirrors’ the swelling of the fetus and placenta. Pre-eclampsia can also develop as part of a “mirror” syndrome. Birth is usually required to induce remission of maternal symptoms.
  • Fetuses with hydrops need to be evaluated very carefully with a detailed ultrasound, fetal echocardiography, blood tests, amniocentesis and genetic work-up.


Fetal hydrops is a serious condition defined by the accumulation of abnormal fluid. It is typically diagnosed during a routine ultrasound examination.

It can be divided in two major categories: immune and non-immune.

Immune hydrops is caused by antibodies developed by Rhesus (Rh) negative blood type mothers being exposed to Rh-positive fetuses. This incompatibility may be prevented if the mother takes Rhesus immune globulin (RhIG) during and after pregnancy.

Non-immune hydrops (NIH) has many possible causes, including:

  • Conditions causing anaemia (low blood count) including fetal haemorrhage (bleeding) or alpha-thalassaemia (disorder of red blood cell structure).
  • Congenital infections (infections that the mother contracts in pregnancy and passes to baby) such as Parvovirus B19 (“Fifth disease” or “slapped cheek syndrome”), Cytomegalovirus (CMV), Toxoplasmosis or syphilis.
  • Fetal birth defects that affect heart function (includes defects that compress the heart or make it work harder such as congenital diaphragmatic hernia (CDH), cystic adenomatoid malformations (CCAM), or fetal tumors such as sacrococcygeal teratoma (SCT)) or that affect the heart rhythm (arrhythmias).
  • Genetic syndromes, chromosomal disorders (such as Turner or Down’s syndrome) or metabolic disorders.
  • Twin-twin transfusion syndrome (TTTS).
  • Unknown causes (these are called idiopathic cases).


Treatment for fetal hydrops depends on the cause. Severely anaemic fetuses can have a blood transfusion in-utero. Fetal arrhythmias can be treated with medication. Thoracic malformations can be treated with a pleuro-amniotic shunt in carefully selected cases.

Referral Information

All patients with fetal hydrops should be urgently referred to a tertiary care centre, such as Mount Sinai Hospital, for evaluation.