Skip to main content

Section 2 - Your blood group and pregnancy

This information is for you if you had your antenatal booking appointment with your community Midwife on or before the 12th May 2024


This section explains the tests that can be done during pregnancy to:

  • find out your blood group
  • find out your Rhesus D group, and
  • look for antibodies.

The people looking after you during your pregnancy need to know your blood group in case you ever need a blood transfusion. It is also important to know your Rhesus D group.

This animation gives information on the screening tests you will be offered during pregnancy for you and your baby.

What is your blood group?

Your blood group will be one of the following four main groups.

  • Group O
  • Group A
  • Group B
  • Group AB

You also have another blood group called the D (Rhesus) group. You can be either Rhesus D positive or Rhesus D negative. For example, your overall blood group might be written as ‘O Rh D positive’.

What are red cell antibodies?

Red cells carry oxygen in your blood. Antibodies are your body’s natural defence against anything that your body thinks is foreign. You may form antibodies if blood cells with a different blood group from your own enter your bloodstream.

This can happen because of a blood transfusion or from your baby during pregnancy.

Red cell antibodies can pass from your bloodstream into your baby’s. This can damage your baby’s blood. Sometimes it causes a rare condition called haemolytic disease of the fetus and newborn (HDFN). Symptoms of HDFN include jaundice and anaemia (lack of red blood cells). Affected babies usually need to be admitted to hospital, where treatment includes phototherapy (treatment with light) and sometimes blood transfusions.

The test

The test is a blood test which can be done with other blood tests, usually early in pregnancy. This blood test is offered to you again around the 28th week of your pregnancy.

If you are Rhesus D negative

If you are Rhesus D negative and your baby is Rhesus D positive, and some of your baby’s blood cells enter your bloodstream, your body might produce antibodies to destroy these ‘foreign’ Rhesus D positive blood cells. This sometimes happens during pregnancy, or more likely when your baby is delivered. If you are Rhesus D positive, this problem does not usually happen.

Can haemolytic disease of the fetus and newborn (HDFN) be prevented?

To help prevent HDFN, if you are Rhesus D negative, you will be offered an injection or injections of anti-D immunoglobulin during pregnancy and after delivery if your baby is Rhesus D positive. This can help stop your body making Rhesus D antibodies and reduces the risk of problems in future pregnancies.

What is anti-D immunoglobulin?

Anti-D immunoglobulin (injection) is a blood product made from blood collected from donors.

Is anti-D immunoglobulin safe?

Occasionally anti-D immunoglobulin causes allergic reactions. How it is produced is very strictly controlled, so the risk of a known virus being passed on to you from the donor is very low.

What are the advantages of having screening for my blood group and antibodies?

If you have this test, you will know your blood group and whether you are Rhesus D positive or Rhesus D negative. It is less common to be Rhesus D negative.

The test will also look for antibodies. It is important to know about these so that if you ever need a blood transfusion this could be given safely. Rarely, antibodies present in your blood might carry the risk of affecting your baby as explained above. If this happens you and your baby can be given specialist care.

About 15% (15 in 100) of the population are Rhesus D negative.

What are the disadvantages of having screening for my blood group and antibodies?

Screening is a simple blood test. The only risk would be the same as having any blood test.

Diagnostic tests for blood group and red cell antibodies

The screening test for blood group and red cell antibodies is very accurate. Sometimes you will need extra blood tests if a problem is suspected or found.

If you know that you are Rhesus D negative

Contact your midwife or your hospital doctor (obstetrician) as soon as possible to remind them that you are Rhesus D negative if:

  • you have vaginal bleeding after 12 weeks of pregnancy
  • you have a miscarriage after 12 weeks of pregnancy, or
  • you suffer an injury to your abdomen (for example, an injury from a seat belt in a car accident or by falling over)

If any of these things happen, your body may start to produce antibodies and you may need an anti-D injection.

Other reasons to be offered an anti-D injection

You should be offered an anti-D injection to reduce the risk of you producing antibodies.

This includes if:

  • you have chorionic villus sampling (CVS) or an amniocentesis (invasive tests)
  • you have a miscarriage or after your baby is delivered, or
  • you have an ectopic pregnancy.