Blood tests in pregnancy

Pregnant woman getting blood test

There are numerous blood tests that need to be carried out when you're pregnant so that you have the best possible chance of a healthy pregnancy and healthy baby

Most of the blood tests will be done in one go at your booking appointment at around 12 weeks, and will involve your midwife taking a few vials of blood. If you have an objection to your blood being tested, talk it over with your midwife – it's your choice which tests you have done.

These are the things the blood will be tested for:

Rhesus status

It is important to find out your Rhesus status and whether you are rhesus negative (RhD negative), which means that your red blood cells lack the D antigen. If you are one of about 15% of people in the UK who are rhesus negative your blood may not be compatible with you baby's blood, and this can cause an immune response where antibodies attack the baby's blood.

This doesn't normally occur during a first pregnancy, but knowing you are RhD negative can help you avoid problems in future pregnancies. If you already have the antibodies in your blood stream, your pregnancy will be monitored carefully to make sure your baby is not harmed. If not, your blood will be tested again for antibody status around 28 weeks.


You will be tested for anaemia at your booking appointment and again at 28 weeks. Anaemia is caused by iron deficiency and may mean that you need iron supplements to meet the demands of both you and your growing baby.

Rubella (German measles) immunity

Most women will have been immunised against rubella when they were at school or as part of their MMR injections, but it has been found that this injection will not give you immunity for as long as was previously thought.

If you have rubella when pregnant, it can cause miscarriage and birth defects. Ideally, your immunity should be checked before you think of conceiving, but if that's too late, it's best to avoid anyone who might have the disease (thankfully, it's fairly rare these days).


I thought everything was fine until I had blood taken at 28 weeks, and it turned out I was severely anaemic. I hadn't realised and thought I was just tired and run down due to being pregnant. I'm now taking huge amounts of iron to ensure there aren't any problems.

This is a sexually transmitted infection (STI) that can remain dormant for years and you can pass on to your baby during pregnancy. If left untreated, syphilis can cause miscarriage, stillbirth or premature birth.


Chlamydia is another STI that has no symptoms, so you will be unaware that you have it, but it can be treated fairly simply. Women under 25 are more likely to have this infection. In pregnancy, there's a risk it can cause pneumonia and eye infections for your baby, and premature birth.


Hepatitis B causes liver problems and, again, you can have it without knowing as it can be symptomless. It can be passed onto your baby but this can be prevented by an injection at birth. You may also be tested for hepatitis C.


HIV is the virus that can lead to AIDS. It can be passed to your baby but the risk of transmission can be greatly reduced during pregnancy and birth if certain precautions are taken. You will receive specaialist care if it turns out you have HIV.

Sickle cell and inherited blood diseases such as thalassaemia

Sickle cell is a serious genetic blood disorder that is most common in people who are Black African or Carribean. Thalassaemia is more common in people of Asian or Mediterranean origin. You can be tested to see if you are a carrier for these diseases in early pregnancy (preferably before 10 weeks). Your partner can be tested, too. There are further tests that can be carried out on your foetus during pregnancy that can tell you if your baby has inherited the disease.

Gestational diabetes

If you are at high risk of gestational diabetes (which only occurs in pregnancy) you will be given a glucose tolerance test, which involves two blood tests after fasting, at 28 weeks or earlier. Those at risk are women who are overweight, have a family history of diabetes, have had gestational diabetes before, or previously given birth to a large baby (more than 9.9lb). Women of south Asian, black Carribean or Middle Eastern origin are more at risk of gestational diabetes.

Tay-Sachs disease

Tay-Sachs is a rare, fatal genetic disease that causes severe degenerative physical and mental disabilities. It is most commonly found in people who are of Ashkenazi Jewish origin. Around 1 in 30 people of this origin are carriers of the HEXA gene that causes Tays-Sachs disease. If a mother tests positive, the baby's father will also be offered the test to assess the risk to the baby. Further tests may be offered to check whether the baby has inherited the disease.