Articles

Key takeaways

• Pregnancy screening tests are offered to all pregnant people.
• They help identify potential health issues for you or your baby early.
• All screening tests are optional, and your choice is respected.
• Results help you make informed decisions about further care.

An introduction to pregnancy screening tests

During your pregnancy, you will be offered screening tests. These tests are offered to all pregnant people. They can help find any health conditions that might affect you or your baby.

The tests can help you make choices about further care or treatment. This can be during your pregnancy or after your baby is born. All screening and tests are optional.

You will still receive your antenatal care if you choose not to have any screening tests. Your midwife or doctor will explain what the tests involve. They will also explain how the tests can help you.

Screening for genetic conditions

Screening for genetic conditions is offered to find out how likely it is that your baby has certain conditions. These include Down's syndrome, Edwards' syndrome, and Patau's syndrome. It is the best way to find out whether your baby has any of these conditions.

What are these conditions?

Down's syndrome – This is a genetic condition caused by an extra copy of a tiny structure that holds our genes (a chromosome). In Down's syndrome, there is an extra copy of chromosome 21. This is why it is also called Trisomy 21.

This condition can cause distinctive facial features and varying degrees of learning difficulties. It can also be linked to heart and other health problems.

Edwards' syndrome – This is a genetic condition caused by an extra copy of chromosome 18. It is also known as Trisomy 18. Babies with Edwards' syndrome often have serious health problems and sadly, many do not survive the pregnancy or live for only a short time after birth. If these babies survive they will require extensive medical care.

Patau's syndrome – This is a genetic condition caused by an extra copy of a tiny structure that holds our genes (a chromosome). In Patau's syndrome, there is an extra copy of chromosome 13. This is why it is also called Trisomy 13. Sadly, many babies with this condition do not survive the pregnancy or live for only a short time after birth. If these babies survive, they will need specialist care.

Screening for these conditions is usually done when you are between 10 and 14 weeks pregnant. Having screening is your choice. You can discuss the test with health professionals to help you decide.

The combined test

The first screening test for Down's syndrome, Edwards' syndrome, and Patau's syndrome is called the combined test. It combines a blood test with an ultrasound scan. This test is not harmful to you or your baby.

The combined test has two parts:

• A blood test – This is taken from your arm when you are between 10 and 14 weeks pregnant.
• An ultrasound scan – This measures the fluid at the back of your baby's neck, known as a nuchal translucency scan. It is done during your 12-week scan, when you are between 11 and 14 weeks pregnant.

The blood test measures the levels of two substances naturally found in your blood during pregnancy. These are known as pregnancy-associated plasma protein-A (PAPP-A) and free beta human chorionic gonadotrophin (free beta-hCG).

The nuchal translucency scan looks at the fluid at the back of your baby's neck. Babies with Down's, Edwards', or Patau's syndromes often have more fluid.

Your antenatal team uses the results of your blood test and scan. They also consider your age. Using a validated programme, together these results will work out the chance of your baby having one of these conditions.

Screening for infectious diseases and blood disorders

Screening for infectious diseases

During your pregnancy, you will be offered a blood test for three infectious diseases. These are hepatitis B, HIV, and syphilis. This is part of routine antenatal screening.

You will usually be offered this blood test at your booking appointment with a midwife. It is important to do the test as early as possible in pregnancy, ideally by 10 weeks.

This allows for early treatment if needed. Early treatment can reduce the risk of passing the infection to your baby.

What are these diseases?

Hepatitis B – This virus affects the liver. It can cause immediate and long-term illness. It is passed on through blood and other body fluids. If you have hepatitis B, your baby will need a course of vaccinations. This greatly reduces their risk of developing Hepatitis B.

HIV – This is a virus that weakens the immune system. It makes it hard to fight off infections. HIV can be passed to your baby during pregnancy, birth, or breastfeeding if untreated. Specialist care and treatment can greatly reduce this risk.

Syphilis – This is a bacteria that is usually passed on through sexual contact. It can also be passed to a baby during pregnancy.

If left untreated, syphilis can cause serious health problems for your baby. In some sad cases, it can lead to miscarriage or stillbirth. Syphilis is treated with antibiotics.

Why are these tests recommended?

These tests are recommended to protect your health and reduce risks to your baby, partner, or family. If you test positive, your partner and other family members or contacts may be offered a test too.

Screening for sickle cell and thalassaemia

Sickle cell disease and thalassaemia are conditions passed down through families that affect the blood (known as inherited blood disorders). They affect haemoglobin, which carries oxygen in the blood. People with these conditions need specialist care throughout their lives.

Screening is offered to find out if you are a carrier of a gene for sickle cell or thalassaemia. This helps determine if you could pass these conditions to your baby.

How are these conditions inherited?

Genes are codes in our bodies. We get one gene from each parent for things like eye colour and blood group.

You only have sickle cell disease or thalassaemia if you inherit two unusual haemoglobin genes. One gene comes from your mother and one from your father.

People who inherit just one unusual gene are called carriers. Carriers are healthy and do not have the disease.

If both parents are carriers, there is a 1 in 4 chance the child will have the disease. There is a 2 in 4 chance the child will be a carrier. There is a 1 in 4 chance the child will not have or carry the disease.

Who is offered screening?

All pregnant people in the UK are offered a blood test for thalassaemia. Not all pregnant people are automatically offered a blood test for sickle cell. In areas where haemoglobin diseases are more common, all pregnant people will be offered a sickle cell test.

In other areas, a questionnaire is used to identify your family origins and the baby's father's origins. If this shows a risk of being a sickle cell carrier, you will be offered a test. You can ask for the test even if your family origins do not suggest a high risk.

This blood test is best done before you are 10 weeks pregnant. If you are found to be a carrier, your baby's father will also be offered a blood test. This allows for further tests to find out if your baby will be affected.

Understanding your screening results

Genetic conditions

Screening for Down's syndrome, Edwards' syndrome, and Patau's syndrome does not give a definite 'yes' or 'no' answer. It tells you if your baby has a 'lower chance' or a 'higher chance' of having the condition.

If your baby has a higher chance, you will be offered a diagnostic test. These might include:

• A test that takes a tiny sample of the placenta (chorionic villus sampling, or CVS).
• A test that takes a small sample of the fluid around your baby (amniocentesis).

These tests give a more definite answer.

If diagnostic tests show your baby has a condition, you will receive support for any decisions you make. This includes decisions about continuing or ending the pregnancy.

Infectious diseases

Screening tests for HIV, hepatitis B, and syphilis are very accurate. These tests will show whether you have these infections. If the test is positive, you will be offered further tests and examinations.

Specialist doctors will help you find the treatment you need. Early specialist care and treatment can protect your health. It can also reduce the chance of your baby getting infected.

Sickle cell and thalassaemia

Screening tests for sickle cell and thalassaemia will tell you if you are a carrier or have these conditions. They do not tell you if your baby has the condition.

If you or the baby's father is a carrier or has the condition, you will be offered diagnostic tests. These tests can find out if your baby is affected.