BLOOD GROUPS IN PREGNANCY
Everybody has one of four blood types (A, B, AB or O). You inherit your blood group from a mix of your parents’ genes. These blood types are further identified as being either RhD positive or RhD negative. This Rhesus factor (RhD) indicates if you have a protein known as D antigen on your red blood cells surface. Around 15% of people in Australia have a negative blood type, that is, they lack the D antigen. If your blood group is RhD negative it is not usually a problem unless you are pregnant and your baby happens to be RhD positive. If an RhD negative person is exposed to RhD positive blood they can develop immunity (via antibodies) to the RhD antigen. One of the first tests a pregnant woman should expect is a blood group test. This test checks her blood group and Rh factor. Her Rh factor may play a role in her baby’s health so it is important to know this information early in pregnancy.
If a pregnant woman is RhD negative and her partner is RhD positive there is a chance that the baby could also be RhD positive. A small amount of the baby’s blood may enter the mother’s blood stream during pregnancy or birth leading the mother to produce antibodies against the Rh positive cells. This is called a sensitising event.
· Blood transfusion with Rh positive blood
· Ectopic pregnancy
· Invasive tests during pregnancy such as a CVS or amniocentesis
· Abdominal trauma
· An external cephalic version where to doctor tries to turn the baby from a breech position
· During labour or birth
· Sometimes the cause is unknown
A sensitising event does not affect the first pregnancy but if the woman has another pregnancy with an Rh positive baby her immune response will be greater and she may produce a large amount of antibodies. These antibodies can cross the placenta and destroy the baby’s blood cells leading to a condition called Rhesus disease or haemolytic disease of the newborn. This can lead to anaemia, jaundice, brain damage and sometimes death to the baby. This however is extremely rare.
Rhesus disease is uncommon these days because it can be prevented by using injections of a medication called anti D immunoglobulin. The medication will remove any RhD positive cells that enter the maternal blood stream and prevent immunity from developing. If you are Rh positive then you do not need to worry about Rh disease. It is routine practise therefore, to offer all RhD negative mothers anti D immunoglobulin injections during pregnancy; two doses, one at 28 weeks and one at 34 weeks’ gestation, and after delivery if the baby is RhD positive. A blood sample is taken from the umbilical cord at birth to check the baby’s blood group. You may require an injection of anti D earlier in the pregnancy if, for example you have had any vaginal bleeding during your pregnancy.
Dr Len Kliman is one of Melbourne’s most experienced and respected obstetricians and gynaecologists.
With over three decades of experience, Dr Kliman has treated tens of thousands of gynaecological patients and delivered over 20,000 babies and still counting!
In 2017, Dr Kliman was awarded an Order of Australia (OAM) for his services to obstetrics and gynaecology.