What are blood types?
Everybody has one of 4 blood types (A, B, AB or O). You inherit your blood group from your parents.
These blood types are further identified as being either positive or negative. For example, your blood type can be A positive or A negative. The ‘positive’ or ‘negative’ shows your 'Rhesus factor' (RhD), which identifies if you have a protein known as 'D antigen' on the surface of your red blood cells.
Why is your blood type important during pregnancy?
Being RhD negative isn’t usually a problem unless you are pregnant and your baby happens to be RhD positive. This can happen if the baby’s biological father is RhD positive.
Around 17 in every 100 people in Australia have a negative blood type.
Your baby’s blood type is inherited from both parents. For this reason, a baby may have a different blood type to its parents. This is normal and usually not a problem. However, in some cases, these differences can be very important.
If your blood type is RhD negative, and your baby’s RhD positive, problems can occur if a small amount of your baby’s blood enters your bloodstream during pregnancy or birth. This is called a 'sensitising event' and can lead to a condition in an unborn baby and newborn, called haemolytic disease of the newborn. Both will be explained below.
What is haemolytic disease of the newborn?
Haemolytic disease of the newborn is a condition in an unborn baby and newborn that can happen if a small amount of your baby’s red blood cells cross the placenta into your bloodstream. This causes your immune system to react by producing antibodies to destroy your baby’s red blood cells. If these antibodies develop, they will not normally affect your first pregnancy.
Your immune system, however, has a good memory, and can produce high levels of these antibodies if there is contact with RhD positive blood in a future pregnancy.
This may lead to serious complications for your baby, such as severe anaemia, brain damage and even death in some cases.
Due to the potential serious effects of haemolytic disease of the newborn, prevention is the key.
Can haemolytic disease of the newborn be prevented?
Haemolytic disease of the newborn is uncommon these days. This is because it can usually be prevented with injections of a medicine called 'anti-D immunoglobulin'.
If you have RhD negative blood, you may also be offered an injection of this medication if there is any concern that your baby’s blood may have crossed the placenta into your bloodstream. This is known as a 'sensitising event'.
What is a sensitising event?
A ‘sensitising event’ can occur:
- during some tests you may have during your pregnancy (such as chorionic villus sampling (CVS) or amniocentesis)
- after miscarriage or termination
- obstetric haemorrhage (heavy, frequent bleeding during pregnancy)
- after an injury or accident to your abdomen
- if your baby is in a breech position and you have an external cephalic version (where doctors turn the baby around inside the womb)
- during labour
- from an ectopic or molar pregnancy
When might I be offered an anti-D injection?
The anti-D injection is safe for both you and your baby.
The anti-D injection may also be recommended if there is concern about a sensitising event (see above).
If you have already developed anti-D antibodies in a previous pregnancy you won’t need another injection in your next pregnancy. Your future pregnancies will be monitored more closely than usual, as will your baby after birth.
There is not enough evidence to suggest that RhD negative women who experience bleeding in their first 12 weeks of pregnancy need anti-D. However, if the bleeding is repeated, heavy or associated with abdominal pain or significant pelvic trauma, anti-D may be recommended.
Currently, the only way to find out if your baby is RhD positive is after they are born and their umbilical blood tested. If your baby’s blood is found to be RhD positive after birth a further dose of anti-D may be offered to you.
Can haemolytic disease of the newborn be treated?
If an unborn baby does develop rhesus disease, it can be treated. The recommended treatment will depend on how severely your baby is affected.
After birth, your baby will likely be admitted to a neonatal intensive care unit (a hospital unit that specialises in caring for newborn babies).
Treatment for haemolytic disease of the newborn after birth can include:
- light treatment (known as phototherapy)
- blood transfusions
- an injection of a solution of antibodies (intravenous immunoglobulin, also known as IVIG) to prevent red blood cells from being destroyed
If haemolytic disease of the newborn is not treated, severe cases can lead to stillbirth. In other cases, it could lead to brain damage, learning difficulties, deafness and blindness. However, treatment is usually effective and these problems are uncommon.
Resources and support
If you have any questions about the risks and benefits of anti-D, or your treatment generally, speak to your doctor or midwife.
Speak to a maternal child health nurse
Call Pregnancy, Birth and Baby to speak to a maternal child health nurse on 1800 882 436 or video call. Available 7am to midnight (AET), 7 days a week.
Learn more here about the development and quality assurance of healthdirect content.
Last reviewed: August 2023