Rhesus Antibodies Test

What is a Rhesus antobodies test?

Rhesus antibodies (Rh Ab’s) is a blood test to determine whether a woman has produced antibodies to the Rhesus antigen. This has important implications for pregnancy and the wellbeing of the unborn foetus.

How is a Rhesus antibodies test performed?

A few millilitres of blood from a vein is required.

When would you need a Rhesus antibodies test?

Rhesus antibodies are produced by a Rhesus negative woman in response to exposure to Rhesus antigens in the blood of her Rhesus positive baby.

The ‘positive’ or ‘negative’ part in a person’s blood group (eg O positive, AB negative, etc) refers to whether their blood cells carry the Rhesus protein.

Rhesus negative individuals will react to the Rhesus protein by producing antibodies against it.

This may occur with a relatively minor leak of baby’s blood into the mother’s bloodstream across the placenta, so-called feto-maternal haemorrhage. A small amount of Rhesus protein can sensitise the woman’s immune system to produce a large amount of antibody to the Rhesus antigen.

In a susbsequent pregnancy, these antibodies can cross the placenta to destroy the red blood cells of an unborn baby, if that baby’s blood group is Rhesus positive. This problem only occurs in Rh-negative women, who carry an Rh-positive baby. It is usually not significant for that particular pregnancy, but may cause serious anaemia (low blood count) in a second or subsequent pregnancy with another Rh-positive baby. This is called Haemolytic Disease of the Newborn (HDN) or Hydrops Fetalis in its most severe form.

Thankfully this is a rare occurrence in modern times, with the preventive treatment available. Anti-D Immunoglobulin is given as an injection to Rhesus-negative women who experience an event that may cause a small amount of baby’s blood to cross the placenta, including:

  • Threatened or actual miscarriage (vaginal bleeding in pregnancy),
  • Abdominal injury, or some procedures such as amniocentesis, Chorionic Villus Sampling or External Cephalic Version (ECV).
  • Anti-D antibodies “mop-up” any foetal blood cells (with the Rhesus protein, or D-Antigen, attached) and prevent the mother’s immune system itself from producing Rhesus antibodies.

Rhesus antibodies test results explained

The presence of Rhesus Antibodies (Rh Ab’s) suggests a risk of Haemolytic Disease of the Newborn (HDN) in a subsequent pregnancy.

Related specialists

Related procedures

  • Blood Test (venesection)
  • Amniocentesis
  • Chorionic Villus Sampling
  • External Cephalic Version (ECV)

Related tests

Also known as

  • Anti-D Antibodies



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