Your blood count, blood group and Rhesus status

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

Full blood count

This measures the level of haemoglobin in your blood. Haemoglobin is part of the blood that carries oxygen around the body.

If it's low it means you could be anaemic. You may be offered iron tablets or other treatments which will help your health and the health of your baby.

You may also be offered other tests.

Blood group and Rhesus status

Everyone has a blood group. You’ll be Group O, A, B or AB and either Rhesus (RhD) positive or RhD negative.

When you’re pregnant it’s important to know your blood group:

• in case you or your baby need to have a blood transfusion
• so your midwife knows if you and your baby have the same RhD blood group

Your blood group might be the same as your baby’s, but it can be different. If you have different blood groups it may mean you need extra care.

RhD negative blood

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

If you have RhD negative blood and you’re exposed to RhD positive blood from your baby, your body makes anti-D antibodies to fight these different blood cells and destroy them.

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.

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 a RhD negative blood group, anti-D injections can stop these antibodies 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.