Foetal screening and diagnostic tests can detect pregnancy complications and foetal abnormalities. Find out which conditions you and your baby may be tested for.
During pregnancy you will be offered antenatal screening tests which can detect problems including pregnancy complications resulting from a condition affecting the baby.
Pregnancy and foetal screening tests may include blood tests (screening for risks such as sickle cell anaemia) and foetal anomaly scans (such as nuchal translucency measurements looking at the risk of genetic abnormalities including Down's syndrome).
A screening test will give you information about how likely it is that your baby will be born healthy. If the likelihood of your baby being born with a condition affecting their health is high, according to the screening test, you will be offered a diagnostic test, which can give you a definite answer.
Available foetal and pregnancy screening tests
There are a number of foetal screening tests that are offered as part of your antenatal care. this article covers:
- the anomaly scan
- screening for spina bifida
- screening for sickle cell and thalasaemia
- screening for Downs syndrome
- amniocentesis and chorionic villus sampling
- cystic fibrosis.
- non-invasive prenatal diagnosis
Before you make any decisions, it is important that you (and your partner) think about the implications of going ahead with any pregnancy screening tests.
All pregnant women are offered the opportunity to have an anomaly scan between 18 and 21 weeks. The anomaly scan is a detailed pregnancy scan that checks the structure and organs of your baby, including the brain, heart and lungs. The anomaly scan is not 100% guaranteed to pick up a specific problem including the presence of genetic abnormalities. You can ask at your hospital about their detection rates.
Although you do not have to wait for ‘results’, sometimes you may need to have the scan repeated, either:
- because the picture is not clear due to the way the baby is lying or moving or
- because the sonographer would like to refer you to someone with specialist expertise or with better equipment.
There is no evidence to suggest that the ultrasound used in the antenatal scan harms your baby. Pregnancy scans do not use the ionising radiation used in other medical diagnostic procedures, which may carry a small risk to the baby.
The anomaly scan will include a check of your baby’s spine to try to rule out major spina bifida. Spina bifida is also known as a neural tube defect (NTD) which can occur very early on in pregnancy. The disabilities caused by spina bifida range from back pain, weakness in the lower limbs and bowel/bladder problems, to paralysis of the lower half of the body and incontinence.
Taking extra folic acid before you become pregnant and in the first three months as part of a healthy pregnancy diet, could help reduce the likelihood of neural tube defects, such as spina bifida.
Screening for Down’s syndrome and other genetic disorders is offered to all pregnant women. There are different ways of carrying out Down’s syndrome screening tests, and if the screening shows a high risk, then a diagnostic test will be offered.
All pregnant women will be asked questions about their family origins to see if they should be offered a blood test to screen for sickle cell disorder and thalassaemia.
Sickle cell disorder is a genetic abnormality of the blood that affects people from Africa, the Caribbean, the Eastern Mediterranean, Middle East and Asia. The disorder affects the quality of red blood cells. If both the mother and father are found to be carriers of sickle cell gene, they will be offered an amniocentesis or chorionic villus sampling (CVS) to see if their baby has the disease.
Thalassaemia is a genetic abnormality of the blood affecting people from Africa, Asia, the Middle East and the Mediterranean. Symptoms include anaemia and attacks of severe pain. If both the mother and father are found to be carriers of the thalassaemia gene, they will be offered an amniocentesis or CVS to see if their baby has the disease.
Cystic fibrosis affects the internal organs, especially the lungs, pancreas and digestive system, by clogging them with thick sticky mucus. Cystic fibrosis is a potentially life-threatening, genetically inherited disease.
If a couple are both carriers of the cystic fibrosis gene, the baby has a one in four chance of having cystic fibrosis. There is no routine UK-wide antenatal screening for cystic fibrosis. However, for those who know they are at risk, an antenatal test is available – a chorionic biopsy carried out at around nine weeks after conception or amniocentesis at about 15 weeks – to identify if the unborn baby has cystic fibrosis.
Babies are screened postnally for cystic fibrosis at around six days by the ‘blood spot’ or Newborn Screening Test.
Amniocentesis and CVS are diagnostic tests you may be offered if your medical history or screening result puts you at high risk of having a baby with a number of genetic conditions. Neither CVS or amniocentesis can check for all chromosomal or genetic problems.
CVS is a diagnostic test which is usually performed between 11 and 13 weeks of pregnancy to find out whether your baby has Down’s Syndrome or another genetic abnormality. A tiny tissue sample is taken from the chorionic villi of the placenta with a needle guided by an ultrasound scan. The procedure takes about 20 minutes, and you may be advised to go home and rest for about 24 hours afterwards. There is a risk of miscarriage of between 1 and 2 in 100 procedures.
An amniocentesis test is a diagnostic test that may be offered to women considered at a higher than average risk of having a baby with a condition such as Down’s syndrome. The test is usually carried out after 15 weeks of pregnancy to find out for certain whether your baby actually has a certain condition. A tiny sample of amniotic fluid is collected through a needle that is guided by an ultrasound scan. The amniotic fluid contains cells that have been shed from your baby. The cells from this sample are then sent to a laboratory where they are grown so that the baby’s chromosomes can be checked.
Unlike a screening test, an amniocentesis is an ‘invasive’ test and carries a risk of miscarriage. It is estimated that of every 1000 procedures about four women will miscarry as a result.
In November 2016, following a clinical recommendation by the UK National Screening Committee, a non-invasive prenatal test for Down’s, Edwards’ and Patau’s syndromes, was approved.
From 2018, the NHS will offer women a non-invasive prenatal test (NIPT) screening test as an alternative to the invasive tests. The main advantages of NIPT are that it can be carried out much earlier in pregnancy compared to current tests and that the procedure does not carry any risk of miscarriage. The test only requires a blood test from mum, rather than having to take a sample directly from the womb as in other types of prenatal diagnosis, such as chorionic villus sampling (CVS) or amniocentesis.
Women can get false positive results though and it is likely that invasive testing will still be required to confirm a positive NIPT result. However, by introducing NIPT the number of women being offered and taking up the invasive test is likely to fall significantly.
There are currently private providers who offer NIPT (you may have heard of the Harmony Test, for example).
Last updated: November 2016
NCT's helpline offers practical and emotional support in all areas of pregnancy, birth and early parenthood: 0300 330 0700. We also offer antenatal courses which are a great way to find out more about birth, labour and life with a new baby.
The NHS gives information on its website about the Sickle Cell and Thalassaemia Screening Programme.
The Sickle Cell Society offers information, counselling and caring for those with Sickle Cell disorders and their families.
The Association for Spina Bifida and Hydrocephalus is Europe’s largest organisation dedicated to supporting individuals and families as they face the challenges arising from spina bifida and hydrocephalus. The website includes information on folic acid and the prevention of spina bifida.
Go Folic! is a campaign led by the Association for Spina Bifida and Hydrocephalus and Scottish Spina Bifida Association, calling on women to take folic acid during and prior to pregnancy.
Mencap supports the 1.4 million people with a learning disability in the UK and their families and carers. Mencap fights to change laws and improve services and access to education, employment and leisure facilities, supporting thousands of people with a learning disability to live their lives the way they want.
The Cystic Fibrosis Trust offers information about the causes, symptoms and treatments of CF along with details about day to day living with Cystic Fibrosis. Helpline: 0300 373 1000.
RCOG (Royal College of Obstetricians and Gynaecologists) offers a guidance sheet about amniocentesis and chorionic villus sampling.
NHS Choices gives full information on the checks and tests offered in pregnancy.
Healthtalkonline offers shared experiences, videos and stories from 37 women and 8 couples from the UK. Topics include making decisions about screening, including those that have and have not ended the pregnancy.
Antenatal Results and Choices is a national charity that provides information to expectant and bereaved parents throughout and after the antenatal screening and testing process. Telephone helpline: 0845 077 2290