Harmony prenatal test

Most accurate and safe test to screen a fetus for genetic conditions.

Research suggests that the Harmony prenatal test is the most accurate, non-invasive method to screen a fetus for risk of Down's syndrome. People with Down's syndrome have an extra chromosome 21 in their cells.

Scientists have discovered there is a small amount of a baby’s DNA ("cell-free" fetal DNA) in their mother's blood. This DNA is thought to come from the placenta. By analysing a sample of blood from the mother, the test can work out the number of chromosomes in the baby.

Why you might need it

By comparison, other prenatal tests such as chorionic villus sampling or amniocentesis require a needle to be inserted into the womb and therefore carry a risk of miscarriage.

All patients, either insured or paying for themselves, can gain rapid access to some of the latest generation diagnostic imaging and treatments.

Find a Spire hospital offering this treatment

Who will do it?

Our patients are at the heart of what we do and we want you to be in control of your care. To us, that means you can choose the consultant you want to see, and when you want. They'll be with you every step of the way.

All of our consultants are of the highest calibre and benefit from working in our modern, well-equipped hospitals.

Our consultants have high standards to meet, often holding specialist NHS posts and delivering expertise in complex sub-specialty surgeries. Many of our consultants have international reputations for their research in their specialised field.

Before your treatment

You will have a formal consultation with a healthcare professional. During this time you will be able to explain your medical history, symptoms and raise any concerns that you might have.

We will also discuss with you whether any further diagnostic tests, such as scans or blood tests, are needed. Any additional costs will be discussed before further tests are carried out.

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Preparing for your treatment

We've tried to make your experience with us as easy and relaxed as possible.

For more information on visiting hours, our food, what to pack if you're staying with us, parking and all those other important practicalities, please visit our patient information pages.

Our dedicated team will also give you tailored advice to follow in the run up to your visit.

The procedure

We understand that having tests can potentially be a time of anxiety and worry. Our experienced and caring medical staff will be there for you, holding your hand, every step of the way.

You will be seen by a consultant obstetrician or midwife specialist in ultrasound. The nature of your procedure will depend on how far along you are with your pregnancy.

If you are between ten and 11 weeks pregnant:

You will need two visits to hospital. The first visit will be between ten weeks and ten weeks and six days of your pregnancy. You will have an ultrasound scan and also give a sample of blood that will be used for the Harmony test.

Your second visit will be two weeks later, at 12 to 13 weeks, when we will discuss the results of the Harmony test and carry out an early abnormality scan. This scan includes examination of the baby’s major organs including the brain, heart, abdomen, stomach, bladder and limb, and the nuchal translucency (NT) measurement.

A nuchal translucency scan is another test, which can be abnormal in babies who have heart problems or some of the rarer genetic problems that are not detected by the Harmony test. It measures the amount of fluid lying under the skin at the back of the baby’s neck. Babies with Down’s syndrome, heart and other chromosomal abnormalities have an increased amount of fluid here.

If we see any abnormalities, or the NT measurement is over 3.5 mm, we will discuss the implications with you in detail. In the majority of cases, the baby’s organs are normal and the NT is less then 3.5 mm.

It is sometimes necessary to perform an internal (trans-vaginal) scan, depending on the position of your womb and the baby’s position, to get the best views. This involves placing an ultrasound probe in your vagina. Most women find this scan less uncomfortable then a smear test.

If you are between 11 + 2 and 14 + 1 weeks:

You will need one visit to hospital. You will have an early abnormality scan to check the baby’s organs and measure the NT. We will also take a sample of blood from you that will be used for the Harmony test.

If any abnormalities are seen, or the NT is over 3.5 mm, we will discuss the implications with you in detail. In the majority of cases, the baby’s organs are normal and the NT is less then 3.5 mm.

If you are more than 14+1 weeks:

You will only need to make one visit to hospital. You may have already had screening for Down's syndrome and an anomaly scan at 18 to 20 weeks. The Harmony test is still available to you.

We would be happy to review the results of any previous scans and tests, and perform a detailed scan to examine the baby’s organs and growth. We will also take a sample of blood from you that will be used for the Harmony test.


The results of your Harmony test will generally be available within two weeks and we will either give them to you at the time of your second visit at 12 to 13 weeks, or contact you by letter if you're not going to have a second visit.

The result is expressed as high or low risk. A high risk result indicates that the baby has a high risk of Down's, Edwards' or Patau syndrome and this is found in 1% of women. To find out if the baby definitely has one of the syndromes, you will need to undergo chorionic villus sampling or amniocentesis, which carry the risk of miscarriage.

For comparison, combined screening using a blood test and measurement of the baby’s nuchal translucency by ultrasound (the standard NHS test), gives a high risk result in 5% of women.

If your Harmony test results show a low risk, it is very unlikely that the baby has one of the syndromes, but not all affected babies will be detected. If your result shows a high risk, we will contact you by phone and also offer you a visit to discuss your options, at no additional cost.

There needs to be enough cell-free fetal DNA in your blood to be able to provide a result. In 3 to 5% of cases, there is not enough cell-free fetal DNA and another blood sample is required. If this happens, the additional sample will be processed at no extra charge.

The Harmony test does not provide information about other rare chromosomal abnormalities. If the ultrasound scan shows a high nuchal translucency or other physical defects, the risk for some rare chromosomal defects may be high. In such cases, we will discuss the implications and your choices in detail.

The test does not provide information on physical defects such as spina bifida, or information on fetal growth. It is therefore advisable that you have all the usual ultrasound scans during your pregnancy.

Why choose Spire?

We are committed to delivering excellent individual care and customer service across our network of hospitals, clinics and specialist care centres around the UK. Our dedicated and highly trained team aim to achieve consistently excellent results. For us it's more than just treating patients, it's about looking after people.


Important to note

The treatment described on this page may be adapted to meet your individual needs, so it's important to follow your healthcare professional's advice and raise any questions that you may have with them.

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