Rhesus negative blood and the anti-D injection

Being rhesus negative is usually not a problem, but it does affect how your pregnancy is looked after. Here’s why you might be offered an anti-D injection and when.

What does rhesus negative mean?

Your blood group includes a rhesus factor, called D antigen, found on red blood cells. If you have it, you’re rhesus positive. If you don’t, you’re rhesus negative. At your booking appointment your midwife offers a blood test to check your blood group. NHS Lothian says about 15% of people in Scotland are rhesus negative.

Why does it matter?

If you’re rhesus negative and your baby is rhesus positive, a small amount of your baby’s blood can sometimes get into your bloodstream. Your body can then make antibodies to it. NHS leaflets explain that this doesn’t usually affect the current pregnancy, but the antibodies stay in your blood and could cause difficulties in later pregnancies, such as anaemia in a baby.

What is anti-D?

Anti-D is an injection that stops your body making these antibodies. It’s made from donated blood plasma. Leaflets from NHS trusts say the injection is safe and doesn’t affect your unborn baby, and that allergic reactions are rare. They also say that, because it is a blood product, the risk of infection cannot be completely ruled out, though donors are carefully screened.

When is it given?

Routinely during pregnancy. The NHS says you may be offered it at your 28-week appointment. One trust leaflet gives a window of 28 to 34 weeks, and arrangements vary, so ask your hospital.
After events that could mix your blood with your baby’s. Trust leaflets list bleeding in pregnancy, miscarriage, ectopic pregnancy, termination, amniocentesis, abdominal injury such as a fall, and labour. Your team may also offer it after other procedures, such as CVS or turning a breech baby, so ask.
After the birth. Your baby’s blood group is tested. If your baby is rhesus positive, you’ll be offered a further dose. If your baby is rhesus negative, no more is needed.

If you bleed during pregnancy, tell the person who sees you that you’re rhesus negative. See spotting in early pregnancy for when to get help.

It’s your choice

Anti-D is offered, and you can ask questions before deciding. If you’re unsure of your blood group, check your maternity notes or ask your midwife.

Questions people ask

Does it affect my first pregnancy?

NHS leaflets say the antibodies don’t usually affect the current pregnancy but can cause difficulties in later ones. Anti-D is offered to rhesus negative women whose baby may be rhesus positive, including in a first pregnancy.

Is my partner’s blood group important?

It can be. Ask your midwife what applies to you.

Do I need anti-D if I’m rhesus positive?

No.

What if I’m not sure of my blood group?

Check your maternity notes or ask your midwife.