If you have this factor (your midwife/doctor will tell you after a blood test) you are described as being RhD positive, and if you do not have it you are RhD negative. The majority of people are RhD positive but 16 people out of every 100 are RhD negative.

Outside of pregnancy, being RhD negative is only a concern if you need a blood transfusion because if you are given Rh positive blood, a number of reactions can occur such as a rise in your body temperature, a rash and occasionally, more severe reactions which might affect how your major organs function.

Your baby will inherit its blood type from you and your partner, which means if you are RhD negative but your partner is Rh positive, you can carry a baby who is RhD positive. Approximately 10% of all births per year are estimated to be RhD positive babies born to RhD negative mothers. The concern in pregnancy is where there is contact between your RhD negative blood and the blood of your RhD positive baby (an event called feto-maternal haemorrhage). While it is unusual for this to happen as you and your baby both have separate blood circulatory systems, your baby`s blood can come into contact with your blood when you have certain tests in pregnancy, such as chorionic villus sampling and amniocentesis and, more commonly, during labour. Further information about these tests can be found in the Informed Choice leaflet Is my baby alright? Screening in pregnancy...

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