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Your Natural Birth Choices

How Your Blood Type Can Affect Your Unborn Baby

We don’t give much thought to our blood type until there’s a problem.

How many people really give much thought to their blood type? Unless you’ve had a medical problem, I’d say probably not often. When you’re pregnant, however, your blood type can matter quite a lot.

The eight blood types

Everyone belongs to a particular blood type within the ABO classification system. Some are more common than others, with most people belonging to the O positive or A positive group. What type you have is determined by genes from both of your parents. How common is your type?

• O positive: 40%
• O negative: 9%
• A positive: 31%
• A negative: 7%
• B positive: 8%
• B negative: 2%
• AB positive: 2%
• AB negative: 1%

Each type also has a positive and negative. This is the ‘Rh type’ and depends on whether there are certain proteins in the red blood cells.

Problems during pregnancy

A problem can arise when the mother’s blood group is Rh negative and the fetus is Rh positive. There will be no problem when:
• The mother’s blood type is Rh positive and the fetus’s blood type is Rh negative
• The mother’s blood type is Rh positive and the fetus’s blood type is Rh positive
• The mother’s blood type is Rh negative and the fetus’s blood type is Rh negative

What happens?

If there is any transference of blood when the mother’s blood group is Rh negative and the fetus is Rh positive, the mother’s system sees the baby’s blood almost as an allergen. Her body will create antibodies which cross the placenta to attack the fetus’s blood. This can result in haemolytic anaemia – a condition that can prove fatal to the growing baby. Once the mother’s body has become sensitised to this ‘allergen’, subsequent pregnancies could mean she and the next baby are Rh incompatible if that baby happens to be Rh positive.

When blood transfer can occur

It is rare that the mother’s blood will come into contact with the fetus’s during pregnancy. However, there are some instances where it can happen, including trauma to the abdomen, miscarriage, ectopic or molar pregnancy, vaginal bleeding, amniocentesis (when a sample if taken from the amniotic fluid) and also sometimes during birth.

What can be done about it?

It’s not an inevitable disaster if you are Rh negative and your baby is Rh positive. Negative outcomes can only occur when and if the blood of the mother and baby meet – which is not that common.

• If you are Rh negative (you’ll get a blood test at your first antenatal appointment if you’re not sure) and you have vaginal bleeding, let your obstetrician know as soon as possible.
• Get an antibody screening blood test to see if you have developed antibodies.
• Ask about an injection of Rh immunoglobulin to prevent sensitisation.

If you are Rh positive of any blood type, you do not need to take action. If you are Rh negative, speak with a healthcare provider about your concerns.

About The Author

Dr Catherine Harris is a Private Specialist Obstetrician who has helped thousands of women deliver their babies safely. To make an appointment, phone (08) 9243 3500 or visit the website



Your Natural Birth Choices