Your blood count, blood group and Rhesus status

During pregnancy, you'll be offered a blood test to find out your full blood count (level of haemoglobin in your blood), blood group and Rhesus status.

Full blood count

This test looks at the red cells, white cells and platelets in your blood.

This test will confirm if you have anaemia, a condition where you don't have enough healthy red blood cells to carry oxygen around your body. This can be treated with iron tablets and other treatments to support your health and the health of your baby.

You may also be offered other tests.

Blood group and Rhesus status

This test will tell you what blood group you have. People belong to one of four blood groups, called A, B, O and AB. You can ask your midwife how to find out your blood group, and how and when you'll receive your results.

It’s important to know your blood group in case you or your baby need a blood transfusion.

It's also important because substances in the blood called blood-group antibodies can sometimes affect your baby. If these antibodies are found, your healthcare professional will discuss it with you.

Your blood group might be the same as your baby’s, but it can be different.

The test will also show if you’re Rhesus positive or Rhesus negative. If you’re Rhesus positive, you don't need treatment. If you're Rhesus negative, this means you don't have a substance called the Rhesus antigen on your blood cells.

RhD negative blood

About 1 in 6 women has an RhD negative blood group.

If you’re RhD negative, there can be issues if your baby is RhD positive and their blood enters your bloodstream.

This can happen:

• during pregnancy
• when you’re giving birth
• after a miscarriage
• if you bleed in pregnancy for any reason

The next time you’re exposed to RhD positive blood, your body produces antibodies immediately.

This is unlikely to be an issue in a first-time pregnancy but can be serious in future pregnancies.

Anti-D antibodies

If your blood is RhD negative and your baby’s is RhD positive, anti-D antibodies can cross the placenta and attack the baby’s red blood cells.

Although this is very rare if it happens your baby may need treatment after delivery or even before they’re born.

Anti-D injections

If you have an RhD negative blood group, anti-D injections can stop these antibodies from developing. This means there’s less chance your baby will be anaemic.

If you have it:

• you’ll be offered an injection of anti-D at around week 28 of your pregnancy
• your baby will have their blood group tested when they’re born

If your baby's RhD positive, you’ll be offered another injection of anti-D.

Because the benefits of anti-D injections go away after a few months, you may need injections if you get pregnant again.