Rhesus negative blood type during pregnancy: Ask a health question

Our Health Information Line receives calls and emails from women on a broad range of health issues. This regular column features answers to some of them.

Q:  I am six weeks pregnant with my first baby and when I had my routine blood tests it revealed I was rhesus negative. What does this mean for me and my baby?

A:  Everybody’s blood falls into a particular blood group (A, B, AB, O). In addition, blood is further classified as being either positive or negative (referred to as the rhesus status or Rh). The majority of people’s blood is Rh positive but approximately 19% of people have Rh negative blood. If someone with Rh negative blood receives Rh positive blood their body makes antibodies against the ‘foreign’ blood.

Being Rh negative is only an issue in pregnancy if your baby is Rh positive. Your baby’s rhesus status will be determined by you and your partner’s genes. The Rh positive gene tends to be stronger so if a mother is Rh negative and the father is Rh positive the baby is likely to be Rh positive. If the mother and father are Rh negative, the baby will be Rh negative.

During pregnancy, the mother and baby’s blood systems are usually kept separate. However, there are times when a small amount of the baby’s blood can cross the placenta and enter the mother’s blood. While this is most likely to happen during labour and birth, it can also occur during amniocentesis or chronic villus sampling (prenatal testing procedures), a bleed during pregnancy, blunt trauma to the abdomen during pregnancy, or a miscarriage. When the baby’s Rh positive blood enters your bloodstream, your immune system will react by making antibodies against it, as though it were a foreign object. This is referred to as Rh sensitised.

If the baby’s blood enters the mother’s blood in the first pregnancy, it usually doesn’t cause a problem as it takes time for the antibodies to develop. The risk is usually for subsequent pregnancies. If you have a second baby that is Rh positive, your antibodies may cross the placenta and attack the baby’s blood cells, causing the baby to become seriously ill.

While this can all sound very alarming, especially when you are newly pregnant, rest assured that there are preventative treatments that will minimise the risk. You will be given an anti-D injection at 28 and 34 weeks of pregnancy and after the birth of your baby. These injections destroy any Rh positive cells in the blood, preventing the production of antibodies that might harm future pregnancies. Additional anti-D injections will also be given if you have any vaginal bleeding during pregnancy or if you have amniocentesis or chronic villus sampling.

If you live in Queensland and have any further questions regarding your pregnancy, you can talk to one of our midwives on the Health Information Line, 07 3216 0376 or 1800 017 676 (toll free outside Brisbane).

Last updated: March 2017

© Women's Health Queensland Wide Inc. This article was reviewed by the Women's Health Queensland Wide editorial committee. It was published in Health Journey 2017 Issue 1.

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