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Blood Tests in Pregnancy

Written by Amina Hatia RM
Medically reviewed by Marley Hall BA RM Diphe
This resource covers

During your first visit with your midwife – often called the booking appointment, you will have a discussion about your health, your medical history and any family medical history that is relevant, alongside information about yourself and your well-being.  Your midwife will then ask to carry out some checks such as your blood pressure, check your urine and your height and weight.  You will also be advised to have some essential blood test that look for among other things, your blood group and whether you have any infections or diseases.  The blood tests also give a good picture of your unborn baby’s health.

It may feel like a lot of blood tests and the number of vials can feel daunting – don’t worry, it will only involve one needle being inserted into your arm once to fill them all.  Blood tests will vary depending on what your hospital’s policy is – but generally speaking you will be tested for:

Blood group
Your blood group is important to know, just in case you need a transfusion during pregnancy or birth. Blood group O is the most common. Groups A, B, and AB are less so.

Rhesus (Rh) factor
In pregnancy it’s important to know your rhesus status. If you’re rhesus positive (RhD positive), it means that you have a particular protein on the surface of your red blood cells. If you’re rhesus negative (RhD negative), you don’t.

If you’re RhD negative and your baby’s dad is RhD positive, there’s a good chance your baby will be RhD positive too. If so, your body will react if your blood mixes with your unborn baby’s blood by producing antibodies to attack your baby’s red blood cells because they’re a different type to yours.

These antibodies stay in your body forever. Although they won’t be strong enough to affect this pregnancy, they will be primed to attack the red blood cells of any future RhD positive babies that you carry.

You can have injections of a substance called immunoglobulin often called Anti-D at 28 weeks and sometimes again at 34 weeks that can stop your body making antibodies.

A blood test called non-invasive prenatal testing (NIPT) can identify whether or not you and your baby have incompatible rhesus statuses. NIPT is being rolled out nationally.

NIPT means that you’ll only need to have immunoglobulin injections if a rhesus mismatch is found between you and your baby.

Haemoglobin levels
Low levels of haemoglobin can be a sign of iron-deficiency anaemia. Your body needs iron to produce haemoglobin to enable your red blood cells to carry oxygen around your body.

If your results show you are anaemic due to iron deficiency, you will be prescribed iron tablets. This is the best way to ensure your iron levels are high enough while you’re pregnant.

Even if your haemoglobin levels are good, you will be advised on the best sources of iron through your diet to ensure your levels remain so.

Hepatitis B Virus

You will also be checked for the infection hepatitis B. If you pass the disease on to your baby before or after birth, they will need to be protected with a series of injections of vaccine and antibodies, starting as soon as they are born.

Syphilis may be checked for as it is a sexually transmitted disease that can cause abnormalities in your baby if left untreated during pregnancy. Syphilis can also cause miscarriage or cause a baby to be stillborn.

If you have syphilis, you’ll need an urgent referral to a specialist team. Treatment is usually a course of antibiotics. These are safe for your baby. Your baby will need an examination and blood tests after birth, and may need antibiotics too.

All mums-to-be are offered a blood test to detect HIV and AIDS. If you have the infection, steps can be taken to reduce the chance of the virus being transmitted to your baby.

Thalassaemia & Sickle-cell disease.

Sickle-cell disorders in the UK are more common in people of African or Caribbean descent. Similarly, thalassaemia can be common for people whose heritage is from Pakistani, Mediterranean countries, India, Bangladesh or other Asian origin. These blood disorders can make you anaemic and can be passed on to your baby.

Vitamin D

Vitamin D regulates the amount of calcium and phosphate in the body, which are needed to keep bones, teeth and muscles healthy. You may find you are offered a test to check your level of Vitamin D in pregnancy to ensure you have enough.

Our bodies make vitamin D when our skin is exposed to summer sunlight (from late March/early April to the end of September). 

Because vitamin D is only found in a small number of foods, whether naturally or added, it is difficult to get enough from foods alone.

Most people in the UK will probably get enough vitamin D from sunlight and a healthy, balanced diet in the spring and summer, so you might choose not to take a vitamin D supplement during these months.

However, you may be at particular risk of not having enough vitamin D if:

  • you have dark skin (for example, if you’re of African, African Caribbean or south Asian origin)
  • you don’t often expose your skin to the sun – for example, if you always cover your skin when outside or spend lots of time indoors

There have been some reports about vitamin D reducing the risk of coronavirus (COVID-19). But there is currently not enough evidence to support taking vitamin D to prevent or treat coronavirus.


All of the blood tests offered are optional. If you are worried about having your blood taken or do not want certain tests carried out discuss your concerns with your midwife who can explain each test in more detail, so you can make an informed choice on whether or not you want to have it.

It’s natural to be worried about having blood tests, especially if you don’t like needles, or are afraid of what the tests may show. However, bear in mind that blood tests give you and your midwife or doctor important information about your pregnancy and your baby’s wellbeing.

Blood tests can also highlight any problems early on so you and your baby get the right treatment in plenty of time.