Rhesus disease

All blood groups have a Rhesus factor of either positive or negative, which indicates whether or not the Rhesus factor – a protein found in red blood cells – is present in the blood.

Rhesus disease can occur in pregnancy when there’s a Rhesus incompatibility between mother and baby. As approximately 85% of the population is Rh-positive, this condition is unusual but extremely serious when it occurs.

Rhesus disease can only occur when the mother is Rh-negative and the father is Rh-positive; as Rh-negative is a recessive gene and together they will produce an Rh-positive child, this will create an incompatibility between mother and child.

While pregnant, the Rhesus incompatibility doesn’t pose a day-to-day threat but if the Rh-positive blood of the baby enters the system of the mother who is Rh-negative (her system is lacking the Rhesus factor and so her body will consider the baby’s blood as a threat)will have an immune reaction to the Rh-positive blood and begin producing antibodies called Anit-D to protect its system from attack.

Blood can mix during:

  • Miscarriage
  • Birth
  • Abortion
  • Amniocentesis
  • Abdominal trauma during pregnancy

When does Rhesus disease occur?

Rhesus disease rarely affects the first pregnancy as it is extremely unusual for mother and baby’s blood to mix before birth. However, subsequent pregnancies can be adversely affected by the condition when the foetus is Rh-positive and death of the baby is possible.

Can I prevent Rhesus disease?

There is a vaccination, which contains anti-D immunoglobulin, for Rhesus disease available which is given to the Rh-negative mother at the birth of her first Rh-positive baby.

Additionally, it is now recommended that the vaccine also be given at 28 and 34 weeks of pregnancy to discourage the body from producing anti-D antibodies and to provide some protect against Rhesus disease in future pregnancies.

Since the vaccination was introduced, rates of Rhesus disease have dropped by 90% and it is now unusual for babies to be born in the developed world with any complications stemming from the condition.

Treatment of Rhesus disease

  • If Rhesus disease has been identified – blood tests early in pregnancy will pick it up – close monitoring of the pregnancy is essential for the wellbeing of the foetus.
  • Blood transfusions for the unborn baby are sometimes necessary.
  • Delivery of the baby is usually induced as soon as possible.


Even after being vaccinated, it is strongly advised that all Rh-positive mothers have a blood test to measure the level of anti-D antibodies in her blood before falling pregnant. Generally, the higher the anti-D count, the more likely it is that Rhesus disease will occur in future pregnancies.

Treatment of babies born with complications due to Rhesus disease

While some babies are born healthy, it is likely that babies born with complications due to Rhesus disease will be affected by anaemia, jaundice and/or heart problems.

Treating the baby’s damaged blood requires blood transfusions that will introduce new red blood cells into the body – blood transfusions also remove any anti-D antibodies that may have been transferred from the mother.

This article was written by Ella Walsh for New Zealand’s leading pregnancy resource, Kidspot.

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