Does a full blood count detect pregnancy

What is being tested?

The human chorionic gonadotrophin (hCG) test is usually used to confirm or monitor a pregnancy. It is also known as the pregnancy test. It can be a blood or urine test.

This test measures the amount of the hormone hCG in the urine or blood. This hormone is usually present only when a woman is pregnant. It starts being produced by the placenta after the fertilised egg implants in the womb.

Occasionally, women can also get abdominal tumours that produce hCG.

Home pregnancy test kits, which you can buy from supermarkets and pharmacies, test for hCG in the urine. The urine test can detect hCG from around the time of the first missed period.

The blood hCG test may detect pregnancy earlier — from about 1 week after conception.

Why would I need this test?

Your doctor might use the blood hCG test to check if you are pregnant, to confirm a positive urine hCG test or to monitor your pregnancy. The blood test is more sensitive than the urine test and the results can assist your doctor to work out when the baby will be born and discover whether the pregnancy is developing normally or not.

Blood hCG tests are also used to detect or monitor the tumours that produce hCG. If the hCG level goes up, this suggest the tumour is getting bigger. If it goes down, it suggests the tumour is getting smaller.

How to prepare for this test

No special preparation is required.

Understanding your results

Normally, hCG levels rise quickly in early pregnancy. But if something is wrong with the pregnancy, your hCG levels may be higher or lower than expected.

If you have a type of tumour that raises your hCG level, such as a germ cell tumour, your doctor might use the hCG test to see if treatment is working or if the tumour has come back after treatment.

More information

Visit the Pathology Tests Explained website or Pregnancy, Birth and Baby for more information about hCG tests.

Read our ‘Guide to blood testing’ to learn more about blood tests in general with information such as:

what to consider before having the test
what happens during a blood test
results accuracy
blood tests cost

During pregnancy, you'll be offered blood tests to help protect your health and the health of your baby. Blood tests are an important part of your care during pregnancy.

Benefits of having blood tests in pregnancy

Having these tests could help you make decisions about your care and the care of your baby, both before and after birth.

It's your choice whether to have blood tests or not. Your decision won't affect the quality of your care.

When will I have blood tests?

Most of the tests can usually be done at one time, and the midwife will usually take blood from your arm at one of your first visits.

Some tests may be repeated routinely later in your pregnancy. This will be discussed with you.

Read more about how blood tests are done

What will my blood be tested for?

Your blood will be tested for:

full blood count, blood group and Rhesus status (positive or negative)
sickle cell and thalassaemia
infectious diseases (hepatitis B, syphilis and HIV)
Down’s syndrome
Edwards' syndrome
Patau's syndrome

Full blood count, blood group and Rhesus status

During your pregnancy you'll be offered a blood test to:

look at the red cells, white cells and platelets in your blood
find out your blood group (A, B, O or AB)
find out if you're Rhesus (RhD) positive or RhD negative

More about blood count, blood group and Rhesus status

Sickle cell and thalassaemia

Sickle cell and thalassaemia are serious, inherited blood disorders that are passed on from parents to children through altered haemoglobin genes.

People who have these conditions will need specialist care throughout their lives.

Learn more about screening for sickle cell and thalassaemia

Infectious diseases

You'll be offered a blood test for infectious diseases that can affect you and your baby, such as hepatitis B, syphilis and HIV.

These conditions are screened for because simple treatments can reduce the risks to you and your baby.

Read more about screening for infectious diseases

Down's syndrome

In the UK, around 1 baby in every 700 born has Down's syndrome. It's the most common chromosomal condition.

You may choose to have tests during pregnancy to find out how likely it is your baby might have Down's syndrome. This will either be a blood test or a combined blood test and scan.

Learn more about screening for Down's syndrome

Edwards’ syndrome

In the UK, around 1 baby in every 5000 births has Edwards’ syndrome. It’s the second most common chromosomal condition.

You may choose to have tests during pregnancy which can help to find out how likely it is your baby might have Edwards’ syndrome. This will either be a blood test or a combined blood test and scan.

Read more about screening for Edward’s syndrome

Patau’s syndrome

In the UK, around 1 baby in every 16,000 births has Patau’s syndrome.

You may choose to have tests during pregnancy which can help to find out how likely it is your baby might have Patau’s syndrome. This will either be a blood test or a combined blood test and scan.

Learn more about screening for Patau's syndrome

Blood test results

You'll usually be able to get your test results at your next clinic visit. All results are confidential.

Occasionally technical problems can occur and you'll be asked to have another sample taken. Some tests are also routinely repeated later in pregnancy.

If further investigation is needed, you'll be contacted as soon as possible and given advice and care.

Your options following a high chance result

If you get a higher-chance screening result for Down's syndrome, Edwards' syndrome or Patau's syndrome, you can choose to have a further screening test (known as NIPT, which stands for non-invasive prenatal testing), a diagnostic test, or have no further tests.

What happens to my blood samples after testing is complete?

Any of your leftover blood samples will be stored in the laboratory for at least 12 months. This is so they can be used in the future if any test results need to be checked.

Medical research

Your personal health information will be kept private, which means it’s only shared with other staff involved in your care. Processes are reviewed regularly to make sure you’re offered the best service possible.

Your leftover blood samples may be used anonymously for other monitoring, laboratory, education and training purposes to improve the quality of patient care. This could be comparing different screening methods and developing new tests. If this happens your personal details will be removed.

Samples that are identifiable to you will never be used without your consent.

If you don't want your stored blood samples to be used for research, please ask the midwife to write ‘no research’ in the comments box on the request form.

You have rights in relation to the access and the use of your personal health information.

Learn more about privacy and confidentiality when using the NHS

Read more about data protection and the NHS

Last updated:
14 March 2022

Can pregnancy be detected in full blood count?

It can find smaller amounts of HCG, and can confirm or rule out a pregnancy earlier than a urine test. A blood test can detect pregnancy even before you've missed a period. Pregnancy blood tests are about 99 percent accurate. A blood test is often used to confirm the results of a home pregnancy test.

What blood level shows pregnancy?

An hCG level of less than 5 mIU/mL is considered negative for pregnancy, and anything above 25 mIU/mL is considered positive for pregnancy. An hCG level between 6 and 24 mIU/mL is considered a grey area, and you'll likely need to be retested to see if your levels rise to confirm a pregnancy.

full blood count detect pregnancy