Blood Type, Rh Factor and Pregnancy

Why it's Important to Know What  Blood Group You Are

All of us have one type of four blood types – A, B, AB or O.  And as an extra bonus, blood types are either positive or negative - this is known as the Rhesus factor (Rh) factor.

If you have a specific protein, also known as an antigen, sitting on the surface of your red blood cells then you are positive and if you don’t, then you’re negative. Thank your parents for whatever blood group you inherited, as well as your Rh factor.

Around 17% of the population fits into the negative blood type category.  Having a negative blood group is generally only an issue during pregnancy, or if someone needs a blood transfusion.

But how will I know what blood group I am?

Early in your pregnancy you will have a range of blood tests. One of these will be specifically to check your type of blood group and see if you are Rh negative.  This is important because if you do have a negative blood group and your baby a positive one, there is a potential for complications to occur with later pregnancies.

If your baby is a negative blood group it’s not a problem, but if your partner is positive there’s a chance for the baby to be positive too.  Around half of all babies born to an Rh negative mother and Rh positive father will be Rh positive themselves.

Generally Rh problems don’t affect firstborn babies. If a mother has subsequent pregnancies with Rh positive babies, then her body will respond more strongly and she will produce more antibodies.  Antibodies are transferred to the baby via the placenta. When this happens the baby can develop anaemia and jaundice.  Other complications can happen such as stillbirth, deafness, blindness, learning problems or brain damage.

During pregnancy, even if only a small amount of the baby’s Rh positive blood enters an Rh negative mother’s bloodstream, (known as a sensitising event), she can produce antibodies against the baby's red blood cells.   This is because her body sees the Rh protein as a foreign substance and she produces antibodies to protect herself.

Sensitising events can happen as a result of:

  • Some testing procedures such as chorionic villi sampling or amniocentesis
  • Miscarriage or termination of pregnancy
  • Abdominal trauma to the mother
  • An ectopic pregnancy
  • The mother having any vaginal bleeding
  • Childbirth, including vaginal and caesarian births.

Is Rhesus Disease a new thing?

No, we’ve known about it for a long time, for at least fifty years, but we’re always learning more about Rhesus disease (Rh Disease) and how to prevent it.   In fact, Australian researchers have led the world in much of the early diagnosis and treatment.

If you do have an Rh negative blood group, this will be marked in your ante-natal record. You will be offered an injection of Anti-D immunoglobulin at 28 and 34 weeks of pregnancy.  If, in-between these weeks you have had what might be a sensitising event, Anti-D will be suggested then.

This injection is given into the muscle, usually the mother’s arm or leg. But the timing of anti-D is important. It needs to be given within 72 hours of a sensitising event, birth, miscarriage or amniocentesis to be effective.

What is Anti-D?

Anti –D  is an immunoglobulin which suppresses the mother’s immune response to the presence of her baby’s positive blood cells.  Anti-D is collected from the plasma of blood donors and has been used for around 30 years in Australia. It’s a low risk and highly effective treatment.

But how will I know what blood group my baby is?

When your baby is born, their blood group will be checked with a sample collected from their cord blood. If they are Rh positive then you’ll be offered another injection of Anti-D to avoid any potential problems in future pregnancies.  Anti-D is low risk and does not carry any complications.

Sometimes, despite everyone’s best efforts, some babies do develop rhesus disease, otherwise known as ‘haemolytic disease of the newborn’ or ‘HDN’. Treatment generally starts with phototherapy to help treat the baby’s jaundice.   An exchange blood transfusion can be necessary and treatment with specific antibodies which help to prevent breakdown of the baby’s red blood cells.

Occasionally, treatment is needed even before the baby is born. A blood transfusion called an intra-uterine foetal transfusion is when they are still “in-utero” and helps to reduce further complications.

Speak with your maternity care provider if you want any more information about your own individual risks.


Jane Barry has qualifications in general, paediatric, immunisation, midwifery and child health nursing. She holds a Bachelor Degree in Applied Science (Nursing) and has almost 30 years specialist experience in child health nursing. She is a member of a number of professionally affiliated organisations including AHPRA, The Australasian Medical Writer’s Association, Health Writer Hub and Australian College of Children and Young People’s Nurses.

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