Blood work and pregnancy go hand in hand throughout antenatal care. From the earliest booking appointment to the later stages of pregnancy, blood tests help healthcare professionals monitor maternal health, identify potential concerns early and make informed clinical decisions. Understanding what these tests involve, when they typically occur and what the results may indicate can help you feel more informed and prepared throughout your pregnancy journey.
This article explains what blood tests during pregnancy are for, what they check at different stages, what the 28-week blood test may involve and how pregnancy blood-test results are generally interpreted — all in plain, accessible language.
What Is Blood Work During Pregnancy?
Blood work during pregnancy refers to the collection and laboratory analysis of blood samples taken at various stages of antenatal care. These tests serve a wide range of purposes: some assess your general maternal health, others look for specific conditions that may affect you or your baby, and some are part of formal antenatal screening programmes recommended by the NHS.
It is important to understand that pregnancy-related blood testing is not a single event. Instead, it is a series of assessments that may take place across different appointments and trimesters, depending on your individual circumstances, the stage of pregnancy and the clinical guidance your maternity team follows.
Blood tests during pregnancy are performed by your GP, midwife or hospital team as part of standard antenatal care. In some cases, individuals may also choose to have additional private blood tests to complement their NHS care — for example, to check specific health markers or to access results more quickly.
Why Are Blood Tests Done During Pregnancy?
Blood tests are performed during pregnancy for a number of important clinical reasons. The overarching goal is to support a healthy pregnancy by identifying any concerns at the earliest possible stage. Specific reasons include:
These are not tests that everyone will automatically receive in identical combinations. The specific blood tests offered to you will depend on your individual health history, risk factors, NHS trust protocols and the stage of your pregnancy.
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Common Antenatal Blood Tests
At your booking appointment — usually around 8 to 12 weeks of pregnancy — a range of blood tests are typically offered as part of routine antenatal care. These commonly include:
Blood Group and Rhesus Factor
Your blood group (A, B, AB or O) and Rhesus (D) status are checked early in pregnancy. If you are Rhesus negative and your baby is Rhesus positive, there is a potential for a condition called Rhesus incompatibility. Knowing this early allows your care team to take appropriate steps to protect future pregnancies.
Full Blood Count (FBC)
A full blood count assesses the different components of your blood, including red blood cells, white blood cells and platelets. During pregnancy, it is particularly useful for identifying anaemia — a common condition in which you have fewer red blood cells or lower haemoglobin than normal — which can cause fatigue and may affect both you and your baby if left unaddressed.
Infection Screening
Blood tests at the booking appointment typically screen for:
Haemoglobinopathy Screening
Depending on your family background and local NHS protocols, you may be offered screening for sickle cell disease and thalassaemia. The NHS Sickle Cell and Thalassaemia Screening Programme aims to identify carriers and affected individuals early so that appropriate support and information can be provided.
Thyroid Function
Thyroid function is not always included as part of routine antenatal blood tests for everyone, but it may be assessed if there are clinical reasons to do so — for example, if you have a history of thyroid conditions or relevant symptoms. Thyroid hormones play an important role in fetal brain development, making their monitoring clinically significant in appropriate cases.
Blood Tests at Different Pregnancy Stages
Blood tests may be offered or recommended at several points throughout pregnancy. Timing is clinically relevant because certain markers are best assessed — or are only meaningfully interpretable — at particular stages.
First Trimester (Weeks 1–12)
The booking appointment involves the broadest initial panel of blood tests. Depending on your preferences and NHS trust, first-trimester combined screening (also known as the combined test) may be offered. This involves a blood test — typically measuring two specific biochemical markers — alongside an ultrasound nuchal translucency scan to assess the statistical probability of certain chromosomal conditions, including Down's syndrome (trisomy 21), Edwards' syndrome (trisomy 18) and Patau's syndrome (trisomy 13).
Second Trimester (Weeks 13–27)
Further blood testing may be offered depending on individual circumstances. Quadruple screening (sometimes called the "quad test") may be offered between approximately 15 and 20 weeks if first-trimester combined screening was not undertaken. This test analyses four biochemical markers in maternal blood to assess the probability of certain chromosomal conditions.
Later Pregnancy (Weeks 28 and Beyond)
Testing continues in the later stages of pregnancy. A repeat full blood count is commonly offered to check for anaemia. Blood group antibody screening may also be repeated. In addition, screening for gestational diabetes may be recommended for those with relevant risk factors.
The 28-Week Blood Test
One of the most commonly asked-about tests is the 28-week blood test. Around this point in pregnancy, it is common for several blood tests to be revisited or introduced.
What the 28-week blood work typically involves may include:
It is important to note that what happens at the 28-week appointment is not identical for every pregnant person. Your midwife or obstetric team will advise which specific tests are appropriate for your individual circumstances, health history and risk factors.
How Many Blood Tests Are Done During Pregnancy?
This is one of the most frequently asked questions about antenatal care. The honest answer is that the number of blood tests during pregnancy varies and cannot be stated as a single fixed number.
As a general guide:
Someone with a straightforward, low-risk pregnancy may have fewer blood tests overall. Someone with a health condition, pregnancy complication or higher-risk pregnancy may have blood tests more frequently throughout their antenatal care. Your midwife or doctor is the most appropriate person to explain which tests are being recommended for you and why.
Pregnancy Screening: What It Means and How It Differs from Diagnosis
Pregnancy screening and diagnostic testing are not the same thing, and this distinction matters enormously when interpreting results.
Screening tests assess the statistical probability or risk of a condition being present. A screening test does not confirm or rule out a diagnosis. For example, a first-trimester combined screening result that indicates a higher probability of a chromosomal condition does not mean that condition is definitely present. It means further investigation — such as a diagnostic test — may be appropriate.
Diagnostic tests, such as amniocentesis or chorionic villus sampling (CVS), can confirm or exclude certain chromosomal conditions with significantly greater certainty. However, these carry small procedural risks and are typically offered only when screening results indicate they may be warranted, or when there are specific clinical reasons.
Understanding this distinction helps manage expectations around screening results. An apparently high-risk result on a screening blood test is not a diagnosis — it is an indication that further clinical discussion and potentially further testing may be needed.
Pregnancy Blood-Test Levels and Interpreting Results
Blood-test results during pregnancy must always be interpreted within the appropriate clinical context. This includes:
What falls within an acceptable range for a non-pregnant individual may differ significantly from what is expected during pregnancy. This is why it is essential that results are reviewed by a healthcare professional with appropriate clinical knowledge — not interpreted using generic online tools or non-pregnancy reference ranges.
If you have received blood-test results and are uncertain what they mean, your midwife, GP or obstetrician is the appropriate person to provide guidance. Private blood testing services, such as those available through Private Blood Tests London, can offer accessible testing for a range of markers, but results should always be reviewed in the context of your broader antenatal care.
Can Blood Work Reveal Pregnancy?
Yes — blood tests can detect pregnancy. While most home pregnancy tests detect a hormone called human chorionic gonadotrophin (hCG) in urine, blood tests can measure hCG in the bloodstream. A quantitative blood hCG test can detect pregnancy earlier than most urine tests and can also measure the level of hCG, which may provide useful information in certain clinical situations.
However, broader pregnancy-related blood work — such as a full blood count, blood group testing or thyroid assessment — is not designed to detect pregnancy itself. If someone has had a positive home pregnancy test but an unexpected result from a different blood test, it is important not to assume one cancels out the other. Different tests measure different things, and any confusing or unexpected combination of results should be discussed with a clinician who can interpret them in the appropriate context.
Blood Work and Fetal Sex
Some individuals ask whether blood tests can reveal the sex of their baby. It is worth distinguishing between routine antenatal blood tests and specific testing methods that may provide this information.
Routine blood tests — such as full blood counts, blood group testing or infection screening — do not reveal fetal sex. However, there are specific non-invasive prenatal tests (NIPT), sometimes called cell-free fetal DNA testing, that can analyse fragments of fetal DNA circulating in maternal blood. These tests can, among other things, provide information about fetal sex and chromosomal conditions with a high degree of accuracy, though they remain screening tests rather than diagnostic tests.
NIPT is not universally offered on the NHS as standard, though it may be available in certain clinical pathways. It is also available privately. If fetal sex information is something you are seeking, it is worth discussing the specific options, their accuracy and their limitations with your healthcare provider or a reputable private testing service.
Blood Pressure and Pregnancy
It is worth clarifying that blood pressure monitoring — while important in antenatal care — is not a form of blood work. Blood pressure is assessed using a cuff, not a blood sample. However, blood tests are often used alongside blood pressure assessment in certain clinical situations.
For example, if your blood pressure is found to be elevated during pregnancy, your midwife or doctor may request blood tests to assess kidney function, liver enzymes, platelet counts and other markers. This is because certain pregnancy-related conditions, such as pre-eclampsia, involve changes that can be detected through blood testing. In this context, blood work complements — rather than replaces — blood pressure monitoring as part of a broader clinical assessment.
How Accurate Are Pregnancy Blood Tests?
The accuracy of blood tests during pregnancy depends on several factors:
It is not appropriate to assign a blanket accuracy percentage to "pregnancy blood tests" as a category, because this grouping encompasses many different types of tests with very different purposes and methodologies. Where specific validated accuracy data exists for a particular test, this should be reviewed in context and discussed with a clinician.
When to Seek Further Advice
If you have received blood-test results that are outside expected ranges, your antenatal team or GP is the appropriate first point of contact. They can explain what the results mean for your specific situation, whether any follow-up testing is needed and what the next clinical steps are.
Private blood testing can be a useful complement to NHS care — for example, for faster access to certain test results or for additional markers not always included in routine testing. You can explore available health screening options and review blood test pricing to understand what is available privately. If you wish to book a private blood test, you can do so directly via the booking page.
Private blood testing does not replace NHS antenatal care and should not be used as a substitute for the professional monitoring provided by your midwife, GP or obstetric team.
Frequently Asked Questions
What blood tests do you have when pregnant?
At your booking appointment, you will typically be offered tests for blood group, Rhesus factor, full blood count, HIV, hepatitis B, syphilis and rubella immunity, as well as haemoglobinopathy screening. Additional tests may be offered depending on your stage of pregnancy, individual health history and local antenatal protocols. Screening tests for chromosomal conditions may also be discussed.
What are blood tests during pregnancy for?
Blood tests during pregnancy serve multiple purposes: checking maternal health, identifying infections, assessing blood group compatibility, screening for conditions such as anaemia and gestational diabetes, and evaluating the statistical probability of certain chromosomal conditions. The aim is always to support a healthy pregnancy by identifying any concerns as early as possible.
How many blood tests do you have during pregnancy?
There is no single fixed number. Most pregnant people will have blood tests at their booking appointment and around 28 weeks, with additional tests depending on individual circumstances, screening choices and health conditions. Your midwife or obstetric team will advise how many tests are appropriate for your pregnancy.
What happens at the 28-week blood test?
Around 28 weeks, blood tests commonly include a repeat full blood count to check for anaemia and a repeat blood group antibody screen. If gestational diabetes screening is indicated, a glucose tolerance test may also be arranged. The specific tests offered depend on your individual circumstances and your maternity team's recommendations.
What does antenatal blood screening check?
Antenatal blood screening encompasses a range of checks. Routine blood tests assess your general health markers, blood group and infection status. Formal screening programmes assess the statistical probability of certain chromosomal conditions. Screening results indicate risk levels rather than providing a definitive diagnosis.
Can blood tests confirm that you are pregnant?
Yes. A blood test measuring human chorionic gonadotrophin (hCG) can detect pregnancy. Quantitative hCG blood tests can identify pregnancy earlier than most urine-based home tests and can also measure hCG levels, which may be clinically useful in some situations.
Can pregnancy blood tests tell the baby's gender?
Routine antenatal blood tests do not reveal fetal sex. However, specific non-invasive prenatal tests (NIPT) that analyse cell-free fetal DNA in maternal blood may provide information about fetal sex alongside chromosomal risk assessment. These are screening tests, not diagnostic confirmations, and availability varies between NHS and private settings.
What do pregnancy blood-test results mean?
Results must always be interpreted in the context of the specific test performed, the stage of pregnancy and the individual's broader clinical picture. A result that appears outside a general reference range may be entirely expected during pregnancy. Your midwife, GP or obstetrician is best placed to explain what your specific results mean.
Are blood tests routine during pregnancy?
Yes, several blood tests form part of routine antenatal care in the UK. The NHS recommends a series of tests at the booking appointment, with further testing at later stages depending on circumstances. Routine does not mean identical for everyone — the specific tests offered may vary.
Why might further blood tests be needed during pregnancy?
Additional blood tests may be needed if routine screening results require follow-up, if symptoms or complications arise, if a condition such as anaemia or gestational diabetes requires monitoring, or if other clinical concerns emerge during the pregnancy. Your antenatal team will explain why any additional tests are being recommended.
What if I had a positive pregnancy test but a different blood result?
A positive home pregnancy test and a different or unexpected blood test result are not necessarily contradictory. Home pregnancy tests and different types of blood tests measure different things. Any confusing combination of results should be discussed with your GP or midwife, who can interpret them in the appropriate clinical context and advise on next steps.
How accurate are blood tests during pregnancy?
Accuracy varies considerably depending on which test is being performed, what it is designed to detect, the stage of pregnancy and the laboratory methods used. Some blood tests are highly sensitive; others are screening tools that assess probability rather than confirming a diagnosis. It is not appropriate to apply a single accuracy figure to all pregnancy blood tests. Your clinician can explain the reliability of any specific test you have had.
This article is intended for general informational and educational purposes only. It does not constitute medical advice, diagnosis or treatment. If you have questions about your pregnancy, blood-test results or antenatal care, please speak with your midwife, GP or obstetric team.