Blood Group and RhD Factor in Pregnancy
A clear explanation of blood groups, the RhD factor, and why knowing yours matters during pregnancy in the UK.
Table of Contents
What Your Blood Group Means
Your blood group is determined by antigens on the surface of your red blood cells. The two main systems tested in pregnancy are the ABO system (A, B, AB or O) and the Rhesus system, specifically the RhD antigen. If you have the RhD antigen you are RhD positive; if you do not, you are RhD negative. Around 15 percent of people in the UK are RhD negative. Knowing your blood group matters because if your blood ever needs to be matched for a transfusion, and because RhD status affects how your pregnancy is managed.
Why RhD Status Is Checked in Pregnancy
If you are RhD negative and your baby is RhD positive (inherited from the other parent), there is a small chance your immune system will produce antibodies against your baby's blood cells. This is called sensitisation. It rarely affects a first pregnancy but can cause haemolytic disease of the newborn in later pregnancies. To prevent this, your midwife will offer Anti-D injections. Your blood group is tested at booking and your antibody levels are checked again at 28 weeks to catch any sensitisation early.
Frequently Asked Questions
Is being RhD negative common?
About 15 percent of people in the UK are RhD negative. It is not an illness, just an inherited blood type, but it does require extra monitoring in pregnancy.
Can my blood group change during pregnancy?
No, your blood group is fixed from birth. However, your antibody screen is repeated at 28 weeks because new antibodies can develop during pregnancy even if your blood group stays the same.
Does my partner need to be tested too?
The NHS does not routinely test partners. If you are RhD negative, your care is based on the possibility that your baby could be RhD positive, so Anti-D is offered regardless of your partner's status.
This information is for educational purposes only and is not a substitute for professional medical advice. Always consult your midwife, GP, or obstetrician about your individual results and care plan.
Further reading:
Related articles: Early Pregnancy Blood Tests | hCG Levels Explained | Anaemia in Pregnancy