Anti-D Injection in Pregnancy: Rhesus Negative Blood Explained

What does Rhesus negative mean?

Your Rhesus status refers to a protein called the D antigen on red blood cells. If you have it, you are RhD positive. If not, RhD negative. Both are normal. The issue arises when an RhD negative mother carries an RhD positive baby. If baby's blood enters your bloodstream, your immune system may produce antibodies against the D antigen. This is called sensitisation.

Why sensitisation matters

If sensitised, your body remembers those antibodies. In a future pregnancy with another RhD positive baby, your immune system could attack the baby's red blood cells, causing haemolytic disease of the fetus and newborn (HDFN), ranging from mild anaemia to severe illness.

Anti-D injections neutralise fetal blood cells that have entered your circulation before your immune system reacts, preventing sensitisation.

When anti-D is given

The NHS offers anti-D through Routine Antenatal Anti-D Prophylaxis (RAADP) at 28 weeks as standard. Some hospitals give two doses at 28 and 34 weeks.

Anti-D is also given after sensitising events: vaginal bleeding, abdominal trauma, invasive procedures (amniocentesis, CVS), delivery if baby is RhD positive, ectopic pregnancy, and molar pregnancy. Contact your maternity unit within 72 hours of any bleeding or injury.

What the injection involves

Anti-D is injected into the muscle of your upper arm or thigh. It takes seconds and feels like any other injection. Mild soreness at the site is common. The anti-D is derived from donated human blood plasma, screened and treated to minimise infection risk.

After the birth

A cord blood sample checks the baby's blood type. If RhD positive, anti-D is offered within 72 hours. A Kleihauer test checks whether extra fetal blood entered your circulation, and an additional dose may be given if needed.

If already sensitised

Anti-D prevents but cannot reverse sensitisation. If booking blood tests show existing anti-D antibodies, your pregnancy will be monitored more closely with additional scans.