Information on Rhesus Factor
What are blood groups?听
Just as every human being is unique, so are the characteristics of your blood. People can belong to one of four blood groups, A, B,听AB听and O which are carried on the red blood cells.听听
There is another听important difference听in people鈥檚 blood called听鈥楻hesus听factor鈥�,听which is also found in the red blood cells. People who are rhesus positive have a substance known as D antigen on the surface of their red blood听cells 鈥� they are said to be听RhD听positive.听听
People who are rhesus negative do not have the D antigen on their blood cells 鈥� they are听RhD听negative. Blood groups and rhesus factors are inherited from a parent. In Europe around 85% of people are听RhD听positive and 15%听RhD听negative.听
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What does this mean for me?听
The听fetal听RhD听status blood test has shown that your baby is听RhD+ve.听Occasionally a few of the baby鈥檚 blood cells听may听enter your blood stream.听Because you are听RhD-ve听the body recognises these blood cells as a听foreign substance and produces 鈥榓ntibodies鈥� against it.听These antibodies are called anti听D.听听This听process听is called sensitisation.听
Usually听antibodies听help to protect the body against harmful things such as bacteria or viruses, stopping them听from growing and causing harm to you.听听Your听baby鈥檚 blood cells听aren鈥檛听harmful to听you听but your body attacks them anyway as it is not used to them.听
In future pregnancies the听anti-D听antibodies can pass through your placenta into the baby and break down the baby鈥檚 own blood cells.听听This results in the baby becoming very poorly and developing a bleeding disorder called听haemolytic disease of the newborn听(HDN).听听听
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How do I prevent these problems?听
An injection of听Anti-D is used to 鈥榤op up鈥� any blood cells from your baby that enter your body.听听This prevents your body detecting听any of baby鈥檚 blood cells and means you听don鈥檛听produce any of your own antibodies.听听As no antibodies are formed nothing crosses the placenta听to听affect the baby.听
We give you anti-D if you have any events that may have increased the risk of baby鈥檚 blood crossing into your blood supply. These are call 鈥榮ensitising events鈥� and include:
- Miscarriage or ectopic pregnancy (complicated)听
- Termination of pregnancy (over 12 weeks)听
- Invasive tests on the baby听听
- Turning baby to head down position听
- Injury to abdomen听
- Bleeding in pregnancy听
- Childbirth including Caesarean section birth听
If you experience any of these events please contact us immediately so we can treat you quickly听
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What is prophylactic anti-D?听
The purpose of any prophylaxis is to prevent something happening.听
There may be times when baby鈥檚 blood crosses into your blood听that we听can鈥檛听detect so听it is听recommended that听all听Rhesus negative听women听pregnant with a听Rhesus positive听baby听are given anti-D prophylactically at 28 鈥� 30 weeks.听听This is based on the evidence of 30,000 women, showing the reduction of sensitisation in women who received this treatment.听听听
One injection is enough to last you 12 weeks so should protect you from听any sensitisation听until delivery.听听It is听effective in 99.8 % of women and听only ineffective in 0.2%,听even less听woman听had听any complications with their baby.听
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Are there any risks?听
Anti-D is made from blood donations outside of the UK.听听It is made from a part of the blood called plasma that is collected from donors. As with all medicines made from blood there is a possibility of a known virus being passed from the donor to the person receiving the anti-D. However, all donors are thoroughly听screened听and the production of anti-D includes steps to remove and destroy viruses ensuring that the chance of passing on a virus is听very low听
There is a small risk of an allergic听reaction听but this is very听rare听and we听monitor听you for 20 minutes shortly after the injection to ensure your wellbeing.听听听
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What happens now?听
We would like to offer you听routine antenatal prophylactic anti-D.听At your听28 week听antenatal check you midwife with take a blood test to check you听don鈥檛听have any antibodies. If you do not have this blood taken and the sample successfully screened you will not be able to have your anti-D.听听You will then attend antenatal clinic and have an injection of anti-D.听
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Do all women need anti-D?听
We recommend that all rhesus negative women听who are pregnant with a baby who is rhesus positive听are given anti-D听but听you may want to decline it in a few situations听(such as those detailed below)听but you will be made aware of the risk.听听听
- If you have opted to be sterilised after birth听and therefore do not want anti-D听听
- If it is certain that you will not have another child after the current pregnancy听听
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If you do not have anti-D听and you develop antibodies it may become a little more difficult to听cross听match your blood at any time in your听life听should you need a blood transfusion听
After听birth听the baby鈥檚 blood will be sampled to听confirm听his/her听blood group.听听If it is听confirmed that baby is听rhesus positive you will听be given another injection of Anti-D known as听postnatal prophylaxis.听听听
We听will also take a blood sample from you for a听Kleihauer听test to see how many of the baby鈥檚 blood cells are in your system so that we can give an听appropriate听sized dose.听听This will ensure that any future pregnancies are protected from you being sensitised.听听
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Bleeding during pregnancy 鈥� what happens?听
Please let any medical staff treating you during your pregnancy know that you are rhesus negative and that you may need anti-D in the case of bleeding or abdominal injury. Should you have a bleed or any other sensitising event in pregnancy please contact the Maternity Assessment Centre. 听
It is safer for you to have anti-D than not to have any.听It is advisable if the bleed is more than 鈥榮potting鈥� to have blood taken for听a听Kleihauer听test,听this will allow us to see if any of your baby鈥檚 blood has flowed into your blood.听It听is important to have your blood taken听to ensure you have been given enough anti-D to听cover the size of bleed.听听
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If you have any further questions about anti-D feel free to ask you midwife or any of the staff at the antenatal clinic.