Your blood type is classified in two ways, through the ABO system and the Rh system.
You are RhD negative when the D antigen is absent from red blood cells, and positive when it is present.
In Australia, approximately 15% of people are RhD negative.
If you are exposed to the D antigen, your body will respond by creating antibodies to fight off the perceived threat to your body.
Identifying your RhD status is important to prevent Haemolytic Disease of the Newborn (HDN) in your baby.
Your baby's blood type is inherited from both you and the baby’s father, so your baby may have a different blood group to you.
Problems can occur when you are a RhD negative blood group and your baby is RhD positive.
During pregnancy, if the baby’s RhD positive blood cells enter your bloodstream this can cause an immune response in you in which your body creates anti-D antibodies against the baby’s Rh positive factor on the baby’s blood.
It is unusual for your first RhD positive baby to become ill as your immune system often doesn’t come into contact with the baby’s blood until labour.
If antibodies are created in your first pregnancy there is a 70% chance that your next pregnancy with a RhD positive baby will be affected. Your antibodies can cross the placenta and can cause HDN which is when the baby’s red blood cells are destroyed, making the baby very sick, causing brain damage and even death.
Your baby’s blood can mix with your blood during what is called a ‘sensitising event’ in pregnancy. These can include vaginal bleeding, miscarriage, abortion, ectopic pregnancy, amniocentesis and trauma to the abdomen, although during labour is the most common time.
It’s important to chat to your Midwife if you experience any of the above events.
Some women can become sensitised from an unknown event.
Anti-D immunoglobulin is a blood product that has been prepared from the plasma of RhD negative donors, all of which who have been immunised against the anti-D antigen.
Anti-D Ig is offered to women with non-sensitised RhD negative blood who may have a baby with Rh-positive blood type.
It is not offered to women who have previously formed Anti-D antibodies or are carrying a known RhD negative baby.
Anti-D is recommended to all RhD negative women at 28 & 34 weeks gestation.
If there is any concern the baby’s blood has mixed with the mother’s blood (a sensitising event), it is recommended within 72 hours.
If the baby is RhD positive, it is recommended within 72 hours of birth.
Anti-D is recommended to be administered in each pregnancy, as it has a limited lifespan.
Anti-D is given as an injection, usually in the upper arm.
The anti-D injection acts to stop the natural antibodies forming in the women’s body, thus protecting the baby.
Anti-D is widely regarded as a safe intervention with very little risk to the mother or baby.
Allergic reactions are very rare but can happen, as well as hypersensitivity including nausea, dizziness and headaches.
As anti-D is a blood product there is potential risk of a viral infection however screening of blood occurs to avoid this risk.