Blood tests are a routine part of antenatal care and help your maternity team build a picture of your health and your baby’s wellbeing throughout pregnancy.
Some tests look at things such as your blood group, iron levels and whether you carry certain infections or blood conditions. Others form part of pregnancy screening and can give you information about the chance of your baby having certain chromosome conditions. Later in pregnancy, some blood tests are repeated to check that things such as your haemoglobin and antibody levels remain healthy.
Most blood tests in pregnancy will not find anything unexpected. But when a test does identify something, finding it early means you can be offered the right information, monitoring, treatment or additional care if needed.
And while it can sometimes look like an alarming number of tubes waiting to be filled, don’t worry — they can usually all be taken from one needle insertion.
When Will I Have Blood Tests in Pregnancy?
You’ll usually be offered blood tests at several points during your pregnancy.
At your booking appointment – usually by around 10 weeks
Your booking appointment is one of your first longer appointments with your midwife.
As well as talking about your health, medical and family history, previous pregnancies, wellbeing and individual circumstances, you’ll usually be offered routine checks such as your blood pressure, urine testing, height and weight.
Your first set of blood tests will usually include:
- a full blood count, including your haemoglobin level
- your blood group and RhD status
- screening for red-cell antibodies
- screening for HIV, hepatitis B and syphilis
- screening for sickle cell and thalassaemia.
Other tests may be recommended depending on your medical history, previous pregnancies or individual circumstances.
Around 10–14 weeks – combined screening
If you choose NHS screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome, you may be offered a blood test alongside an ultrasound measurement taken at your dating scan.
Together, these form the combined screening test.
The combined test uses information from your blood test, ultrasound scan and other factors such as your age to calculate the chance of your baby having one of these chromosome conditions.
Later in pregnancy – usually around 28 weeks
You’ll usually be offered another blood test at around 28 weeks.
This commonly includes:
- another full blood count to check for anaemia
- repeat blood-group antibody screening.
Depending on your blood group and circumstances, this may also be around the time that anti-D treatment is discussed or given.
You may have other blood tests at different points during pregnancy if there is a specific reason – for example to investigate gestational diabetes, itching, high blood pressure, thyroid concerns, infection or symptoms of anaemia.
Not everyone will have exactly the same tests at exactly the same time. Your midwife will explain which tests are being offered to you and why.
What Are All These Blood Tests Looking For?
Full Blood Count and Anaemia
A full blood count looks at several different types of blood cells, including your haemoglobin.
Haemoglobin helps your red blood cells carry oxygen around your body. If your haemoglobin is low, it may indicate anaemia.
Iron deficiency is a common cause of anaemia during pregnancy, but it isn’t the only cause, so your maternity team may arrange additional investigations such as a ferritin blood test if needed.
If you have iron-deficiency anaemia, you may be offered iron supplements alongside advice about increasing iron-rich foods in your diet.
Your Blood Group
Your blood group will usually be checked early in pregnancy.
The main blood groups are:
- A
- B
- AB
- O.
Knowing your blood group is particularly important if you ever need a blood transfusion during pregnancy or birth.
Your blood is also checked for red-cell antibodies because some antibodies can cross the placenta and affect your baby’s red blood cells.
If clinically significant antibodies are identified, you’ll usually be offered additional tests, monitoring and specialist care where appropriate.
Rhesus D Status
Your blood will also be checked to see whether you are RhD positive or RhD negative.
If you are RhD positive, no further routine treatment for rhesus incompatibility is usually needed.
If you are RhD negative, there is a possibility that your baby could be RhD positive.
If some of your baby’s RhD-positive blood cells enter your bloodstream, your immune system may recognise them as different and begin producing antibodies against them. This is known as sensitisation.
These antibodies can cross the placenta and affect an RhD-positive baby’s red blood cells. This can cause haemolytic disease of the fetus and newborn (HDFN).
Fortunately, we can usually prevent sensitisation with anti-D immunoglobulin.
Fetal RHD Testing: Predicting Your Baby’s Blood Group From Your Blood
If you are RhD negative, you may be offered an additional blood test called non-invasive fetal RHD genotyping.
This is a clever test that looks for tiny fragments of your baby’s genetic material circulating naturally in your bloodstream, known as cell-free fetal DNA (cffDNA).
From your blood sample, the laboratory can predict whether your baby is likely to be:
- RhD positive, or
- RhD negative.
If your baby is predicted to be RhD negative, you will not usually need routine anti-D because there is no RhD incompatibility.
If your baby is predicted to be RhD positive—or the result is inconclusive—you will usually be offered anti-D immunoglobulin later in pregnancy.
The timing and availability of fetal RHD testing can vary between maternity services.
HIV
You will routinely be offered screening for HIV early in pregnancy.
If HIV is identified, effective treatment and specialist maternity care can greatly reduce the chance of the virus being transmitted to your baby.
Your maternity team will work alongside specialist services to plan your pregnancy, birth and your baby’s care.
Hepatitis B
You will also be offered screening for hepatitis B.
Hepatitis B can be passed from you to your baby around the time of birth.
If your test is positive, you will be referred for specialist assessment and a plan will be made for your care and your baby’s protection after birth.
Babies who are at risk are offered hepatitis B vaccination soon after birth, with further vaccination and, for some babies, hepatitis B immunoglobulin depending on individual circumstances.
Syphilis
Screening for syphilis is routinely offered during pregnancy.
Syphilis can cause serious complications for pregnancy and your baby if it is not treated, including miscarriage and stillbirth.
The reassuring news is that effective antibiotic treatment is available during pregnancy.
If your screening result suggests syphilis, you will be referred promptly to a specialist team for confirmation, treatment and follow-up.
Sickle Cell and Thalassaemia
Screening for sickle cell and thalassaemia is offered in pregnancy to identify whether you carry a gene variant that could be passed on to your baby.
It is best for screening to happen early in pregnancy, ideally by around 10 weeks, because this gives you more time to understand your results and consider any further testing if needed.
Anyone can carry a haemoglobin variant.
Some variants are more common in people whose family background is from:
- Africa
- the Caribbean
- the Mediterranean
- the Middle East
- South Asia
- Southeast Asia.
However, heritage is only one part of assessing risk, and assumptions should never be made about someone’s risk based solely on how they look or identify.
If you are found to be a carrier, your baby’s biological father may also be offered testing.
If you both carry a relevant gene variant, you’ll be offered specialist counselling to explain your baby’s chance of inheriting the condition and the further testing options available.
What About Vitamin D?
Vitamin D is important during pregnancy because it helps regulate calcium and phosphate and supports healthy bones, teeth and muscles.
However, routine vitamin D blood testing is not recommended for everyone during pregnancy.
Instead, vitamin D supplementation is recommended during pregnancy.
Some people have a greater chance of vitamin D deficiency, including those who:
- have black or brown skin
- have limited exposure to sunlight
- cover most of their skin when outdoors
- spend a lot of time indoors.
You may be offered a blood test if there is a clinical reason to check your vitamin D level.
Your midwife, GP or dietitian can advise you about supplementation or testing based on your individual circumstances.
Will I Have Any Other Blood Tests?
Possibly.
Pregnancy care is individual, and additional blood tests may be recommended depending on your health, symptoms or how your pregnancy progresses.
These might include investigations for:
- gestational diabetes
- pre-eclampsia or high blood pressure
- intrahepatic cholestasis of pregnancy (ICP)
- thyroid conditions
- infection
- iron deficiency
- other medical conditions.
Your maternity team should always explain why a test is being recommended and what the result may mean.
Are Blood Tests Compulsory?
No.
Blood tests and antenatal screening are offered to you rather than compulsory.
You can:
- accept all the tests offered
- accept some and decline others
- ask for more information before deciding
- change your mind later where testing is still possible.
If you’re unsure, ask your midwife:
- What is this test looking for?
- Why is it being offered to me?
- What could the result mean?
- What happens if I choose not to have it?
- What would happen next if the result identifies something?
Your maternity team should give you enough information and time to make a decision that feels right for you.
If You’re Nervous About Blood Tests
Lots of people dislike needles and some are genuinely very frightened of them, so please tell your midwife or the person taking your blood.
There is no need to be embarrassed.
It may help to:
- sit or lie down
- look away from the needle
- use slow, steady breathing
- have someone with you if possible
- tell the person taking your blood if you have fainted previously
- ask them to talk you through what they are doing—or not to, if distraction works better for you!
And despite the number of tubes sometimes needed, they can normally all be filled using a single needle.
Why Are Blood Tests So Important?
Most blood tests in pregnancy come back without anything unexpected.
But when a result does identify something, finding it early can make a real difference.
It might mean treating anaemia so you feel better, providing treatment for an infection, arranging additional monitoring, offering anti-D, or giving you information about your baby so that you can make informed choices about your pregnancy and care.
Blood tests are therefore not simply a checklist of things that have to be done during pregnancy. They are one of the ways your maternity team can make your care more individual to you.
And remember, screening is about offering you information and choices. You should always feel able to ask questions and understand what you are being offered before deciding.
Want to Understand More About Your Antenatal Care?
Our Complete Antenatal Course explores antenatal appointments and screening as well as pregnancy health, preparing for labour and birth, feeding, caring for your new baby and the postnatal period.
The course is self-directed, so you can work through the information at your own pace and revisit it whenever you need to.
Our aim is to help you understand your care, know what questions you can ask and feel confident making informed choices throughout your pregnancy.
References
- NICE. Antenatal care (NG201).
- NICE. High-throughput non-invasive prenatal testing for fetal RHD genotype (HTG420).
- NICE. Routine antenatal anti-D prophylaxis for women who are rhesus D negative (TA156).
- NICE. Maternal and child nutrition: nutrition and weight management in pregnancy (NG247).
- NHS. Your antenatal appointments.
- NHS. Screening tests in pregnancy.
- NHS. Screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome.
- NHS. Screening for sickle cell and thalassaemia.
- NHS. Haemolytic disease of the fetus and newborn (HDFN).
- NHS England. Screening tests for you and your baby.
- NHS England. Infectious diseases in pregnancy screening programme: HIV, hepatitis B and syphilis.
- NHS England. Sickle cell and thalassaemia screening programme.
- NHS Blood and Transplant (NHSBT). Fetal genotyping from maternal blood.
- UK National Screening Committee. Antenatal and newborn screening programmes.
- PIF TICK. Criteria for trustworthy health information.