Rhesus factor is a substance (blood product) found in blood. Approximately 85% of the population has the rhesus factor and the remaining 15% percent do not. It is symbolised by the plus or minus after your blood group, for example, A- is rhesus negative and A+ is rhesus positive.
If you are a mother-to-be with negative (-) blood, there are some things you might like to know if your partner has rhesus positive () blood. This does not apply to mothers with rhesus positive () blood which does not pose any problem.
What if I don't know mine or my partner's blood group?
When you first find out you are pregnant, your doctor/midwife/obstetrician may prescribe some routine tests. If you don't know your blood group or if you're unsure whether the doctor is testing it or not, just ask and this can be easily done.
How can my negative blood be a problem?
If you are rhesus negative and your husband is rhesus positive, then your unborn child may inherit negative or positive blood – you wont know until birth. However if the mother is negative and the foetus happens to be positive (positive being dominant, negative recessive), this may cause problems for the foetus as well as any future pregnancies the mother may have.
Problems can occur if the foetus' positive blood manages to find it's way into the mother's bloodstream, either during pregnancy or labour, mixing with her negative blood. If this happens and it is not treated, the mother's blood can create antibodies to attack the positive blood containing a ‘foreign' component, causing anaemeia or in a worst case scenario, death for a foetus. This means that any future pregnancies the mother has where the foetus is again rhesus positive, her antibodies may cross the placenta and attack the foetus' blood cells.
How can this be prevented?
Your obstetrician or midwife may organise a couple of blood tests throughout your pregnancy to monitor antibodies in your blood. It is important that the hospital where you birth your baby is aware of your rhesus negative blood, so they can test baby's blood after the birth (from the placenta) to discover baby's blood type. Should your baby have positive blood, you can choose to be given an "anti-D" injection within a couple of days following the birth. This prevents antibodies from forming.
If you experience any bleeding during pregnancy or if you have an amniocentesis, miscarriage, ectopic pregnancy or termination, you need to make your primary medical carer aware of this as soon as possible, as these may all pose opportunities for the blood of the foetus to mix with that of the mother's and it will be unclear in most of those cases as to which blood group the baby belonged to. If none of these things happen, in a normal pregnancy, you will not need ‘routine' anti-D injections until after the birth, should the baby's placenta come back as rhesus positive – and if you choose to.
Some Obstetricians are now routinely giving Rh- women Anti-D injections without any blood tests to detect antibodies. However you might like to ask your doctor if this is really going to be effective or worthwhile if you have had no indication to suggest you have been bleeding. Not only is the shot of Anti-D a blood product (which involves risks in itself), but the chances that those routine injections (usually 2-3) will be given to you within 72 hours of possible bleeding – as required after possible exposure – which there has been no indication of bleeding anyway, is very slim. Your baby's circulation is completely separate to yours so in a healthy pregnancy, the chance of the blood mixing is very, very slim.
Being rhesus negative myself and having had two children with my Obstetrician, I didn't have bleeding during pregnancy so was never given preventative anti-D until after the birth, and everything was fine. I have certainly questioned the recent move to do these routine pregnancy shots.
What if I already have formed antibodies against positive blood?
The anti-D injection may not be able to protect you or your baby if you already have antibodies and you will need to be closely monitored by your obstetrician, possibly requiring specialist care. Discuss with your obstetrician.
If I have the anti-D injection will I be protected for good?
No – with each pregnancy the risk still exists of antibodies forming, should positive and negative blood become mixed. It is therefore important to make sure you continue to communicate your blood group with your future medical carers if you decide to become pregnant again.