VeriSeq Illumina NIPT in London  

It’s important for us that you understand the terminology we use for screening tests:

Detection rate is defined as the fraction of all patients who have the disease and are called positive by the screening test.

Positive Predictive Value or PPV is the proportion of the ‘true positives’ as proportion of all positive results. As a practical example, the Panorama AI test has a 95% PPV for Down’s Syndrome, meaning that 95% of the fetuses identified as ‘High Probability’ will statistically have the condition. However, the limitation of the test is that in 5% of the cases, it will result in a ‘false negative’ meaning that the test will return a ‘High Probability’ result for a fetus that doesn’t have Down’s Syndrome.

That’s why, for every High Probability result we would refer the patient for a diagnostic test such as CVS or Amniocentesis to verify the results.

In the past there has been confusion about certain aspects of NIPT – please see this notice. If any of the above still unclear to you, please get in touch with us via email or phone and our friendly stuff will be happy to run you through the characteristics of the test.

We wrote a special blog post about understanding the statistics of the NIPT test,  if you would like to find out more, click here.

Non-invasive prenatal testing (NIPT) or non-invasive prenatal screening (NIPS) is a screening method for determining the chance that a baby will be born with Down’s syndrome or other chromosomal anomalies. NIPT is based on the assessment of small DNA fragments from a baby’s placenta (named ‘cell-free DNA’ or ‘cfDNA’) that are disseminated in the blood of every pregnant mother. Placental cfDNA is usually identical to the DNA of the baby and testing it provides an opportunity for early detection of particular chromosomal anomalies without harming the baby.

Although cfDNA is a relatively new genetic test, it has been proven to be superior to any other screening tests for Down’s syndrome, including the combined screening test (CST) used by the NHS. However, NIPT can detect a relatively small proportion (about 15%) of all fetal anomalies, because the vast majority of fetal abnormalities are physical (structural) and not chromosomal.

NIPT is a screening test, meaning that NIPT cannot definitively answer whether a baby has Down’s syndrome or other tested chromosomal conditions. If the results are positive (high chance), follow-up invasive testing is needed to get a definite diagnosis. Any invasive testing carries a small risk of miscarriage.

Currently NIPT is not routinely offered by the NHS.

The nuchal translucency (NT) thickness measurements scan was developed in the 1990s, and at the time was the best screening option for Down’s syndrome offering about 62% accuracy and a 5% false positive rate. The NHS now offers the ‘combined test’ at 11-14 weeks which includes a nuchal translucency scan along with a blood test (for PAPP-A and HCG proteins) with improved the accuracy of 81% and false positive rate of 4.5%.

NIPT was first introduced in 2011 and was shown to have superior accuracy to the combined test with a 99.99% detection rate and sub 0.1% false negatives. Please note, we still recommend following through with your NHS antenatal appointments, they are important for the continuity of your pregnancy care.

We offer PrenatalSafe NIPT for the following:

• Down’s syndrome (T21)
• Edwards syndrome (T18)
• Patau syndrome (T13)
• fetal sexing

We recommend taking the NIPT along with our comprehensive early anomaly scan (10-week scan) as soon as possible – 10 weeks. Early detection of either chromosomal or structural anomalies allows more time in terms of pregnancy management for those conditions. If your sample fails, you have plenty time for redraw.

If you’re unsure about the age of your pregnancy, we strongly recommend performing a viability scan with us at around 7-8 weeks of your gestation. The viability scan will date your pregnancy and we can arrange the earliest possible appointment for your NIPT.

If you’d prefer not to have the viability scan, please allow a couple of days after the 10-week mark to avoid repeat appointments for drawing the bloods. You can also miss all the advantages of the 10-week scan, because your baby will be too young to have a proper early anomaly scan. 

In theory, NIPT is available from 9-40 weeks, but it is strongly recommended to take the test in the first trimester, as the pregnancy management options in the second trimester can be very limited. 

Following your ultrasound scan appointment, you will receive a detail scan report from our doctors, as a hard copy and a PDF version sent to you via our secure cloud system Tricefy.

As soon as we receive your NIPT test results from the laboratory, our clinician reviews the test results and signs them off. One of our friendly clinical staff will then contact you via a phone call to interpret the test results. We will then send you a soft copy of the test results via Tricefy.

The main advantages of NIPT are related to Down’s syndrome (T21) screening.

They are:

• early testing from 10 weeks
• high negative predictive value for T21
• high detection rate for T21
• low false-positive rate for T21

As any screening test NIPT has some disadvantages.

Here there are the most significant NIPT limitations:

• relative high cost of the cfDNA test (Harmony Test)
• whilst a very sensitive screening test, it is not diagnostic
• cannot detect ANY physical (structural) anomaly
• very limited effectiveness for the babies that have increased nuchal translucency (NT) thickness or physical (structural) anomaly
• processing time of up to a week (or longer in 5% of the cases) or even 10 days for Invitae NIPS
• failure to return a result in up to 5% of women (‘no-call’ results) which is more common for Harmony Test

In case the NIPT result shows a high chance for Down syndrome or other conditions, our doctor will contact you and explain the further steps we advise to take. We will most likely arrange a referral to your NHS fetal medicine unit for further counselling and possible diagnostic test such as CVS or amniocentesis.

Alternatively, we can refer you to a private fetal medicine consultant (consultation cost is not included in our service).

We will also offer early fetal echocardiography for free (regular cost of the examination £320) for all our patients with high chance NIPT for trisomy 21, Di George syndrome, trisomy 18, trisomy 13 and Turner syndrome.

Most pregnant women receive complete results from cfDNA testing, indicating either a high or low probability for aneuploidy.

In about 3% of cases (much more common with a harmony test) we will need to contact you without giving you a test result and ask you to come in for an additional sample of blood or to give us more information about your pregnancy or medical history. There will be no extra cost for an additional mother’s blood test.

It is because in small proportion of blood specimens submitted after 10 weeks gestation there is an insufficient amount of the baby’s cfDNA. This situation is called low fetal fraction. The chance to have low fetal fraction is getting higher with increased maternal body weight. There are other rare factors making NITP results inconclusive.

In the case of a harmony test no-call result, we will discuss options of alternative screening and/or referral for diagnostic testing if you either decline a second attempt at NIPT or do not receive a result after two attempts.

The harmony scan can only be done from a gestational age of 10 weeks, while panorama NIPT can be done from 9 weeks. TDL/Natera do not accept any blood samples for patients below that gestational age. We recommend waiting until a gestational age of 10 weeks + 2 days (9+4 for panorama) to perform the harmony/panorama scan to avoid having to come in more than once.

In case you booked for a panorama/harmony scan, but the ultrasound scan indicated a GA below 9/10 weeks (respectively), we will have to rearrange for you to come in at a later date for an additional cost of £50 to cover for our staffing cost.

In the case of no-call results from the test (about 3% of the cases), we will be happy to schedule in another time to draw another blood sample free of charge. In case of a second no-call result, we will refund the harmony test portion of the appointment charge as per below. If, upon discussion with our clinician, you decide that the harmony test is not the right decision for you, we will refund the harmony test proportion of the appointment and will only charge for the scan.

In the case of inconclusive results for Downs syndrome or trisomies 18 or 13, we are committed to refunding the harmony test cost.

Because the harmony test is being undertaken by a third party, TDL (The Doctors Laboratory), we will contact them to arrange the refund. The refund will be for the harmony test only (we cannot compensate the cost of ultrasound) and will be processed in a few business days.

There is no reimbursement for inconclusive fetal sex results. In those rare cases we will offer you an anatomy and gender scan for a reduced cost and will discuss the findings and need for further referrals.