NIPT – Book Now
£419 / £459 with ultrasound scan
Non invasive prenatal testing
An NIPT test is a blood test that looks for whether your baby has Down’s Syndrome, Edward’s or Patau’s Syndrome. In these conditions there are 3 copies of certain chromosomes instead of 2 (“Trisomy”). The test looks at DNA from the baby that is present in the mothers bloodstream.
You can have an NIPT test at Somerset Early Scans from 10 weeks of pregnancy onwards.
Test performance for Down’s Syndrome
This screening test has a high “sensitivity” for Down’s syndrome (Trisomy 21) of 99.9%. This means that the NIPT test will pick up more than 99% of babies who have Down’s syndrome.
Because the sensitivity is not 100% there is a small chance (less than 1%) that an NIPT test may report a low probability of the baby being affected when in fact the baby does have the condition.
Another aspect of test performance is its “positive predictive value” (PPV). This is the likelihood that a result stating a high chance that the baby has the condition, is correct.
The PPV depends upon the background chance. If you have had a high chance result for Down’s syndrome from an NHS screening test or are in an older age group the positive predictive value will be above 90%. If you are low risk the positive predictive value will be much lower, again the risk depends on factors such as your age. One large study reported the PPV for low risk women to be 82% for Down’s syndrome.
The NIPT company quote PPV of 33-95% depending on the background chance.
Therefore for high chance NIPT test results an invasive test such as amniocentesis or chorionic villus sampling is recommended to give diagnostic results.
Test performance for Edward’s and Patau’s Syndromes
Edward’s syndrome (trisomy 18) and Patau’s syndrome (trisomy 13) are rarer conditions. The reported sensitivity or detection rate for these is 99.9% (T13). The PPV of the test is 23-83% for Edward’s syndrome and 9-67% for Patau’s syndrome.
Reasons for choosing NIPT
The NIPT test is available early in the pregnancy, from 10 weeks onwards.
Many couples now choose to pay for a non-invasive prenatal test (NIPT) because of its high sensitivity for Down’s syndrome.
Another reason for choosing an NIPT is after receiving a non reassuring result for Down’s syndrome from the 12 week NHS screening test. The NHS now offer NIPT free of charge if the chance from their initial test is 1 in 150 or greater. For those who have what they feel is an increased chance, but not as high as 1 in 150, they may opt to have NIPT.
Limitations
Non-invasive prenatal testing does not diagnose other genetic or structural diseases such as spina bifida. A low risk result obviously does not guarantee a healthy baby.
What will happen
We will see you to discuss the pros and cons of testing and take your consent if you decide to go ahead.
We need to have accurate dating of your pregnancy so if you come before your first scan then please book an NIPT test with scan so that a scan for viability & dating will be done followed by your blood test. Please note that it is essential to have had a dating scan before NIPT, the laboratory cannot process results without this. If you have had a scan in another service we can use the dates from that scan.
The samples are sent by Royal Mail Business Post to The Doctors Laboratory in London, who process all the UK NIPT samples in house.
A result will be received within 10 days or less and you will be contacted by us within 24 hours.
In 2% of cases the sample cannot be processed due to it having insufficient DNA within it. In this case we will contact you to arrange repeat testing at no additional charge. This is more likely to happen if you are earlier in the pregnancy or overweight. In a small number of these repeat tests no result will be obtained in which case your laboratory fee will be refunded to you.
Twins & IVF pregnancies
The NIPT test can be used for IVF pregnancies, including those with donor eggs.
It can be used in twin pregnancies for screening purposes but not to look at the sex chromosomes. It cannot be used in twin pregnancies where one twin has not been viable. It is also not validated for use in triplet pregnancies.
Positive tests
If you have a test result reported as high chance we recommend seeing an Obstetrician, or Fetal medicine specialist to discuss the pros and cons of having an invasive test such as an amniocentesis, to provide a diagnostic result. Or to discuss a plan for care during and after the pregnancy. We will seek your consent to contact your Midwife or Obstetrician on your behalf so that this can be arranged.
Why book with us?
We believe in informed choices so we allow plenty of time for a full discussion with you at your appointment.
The clinician who saw you will personally phone you as soon as your results are available.
In the rare event of a high risk report, we will liaise with the NHS team on your behalf, to get you seen quickly.
Other uses for NIPT
The NIPT test can also test for the gender of the baby however a report from the Nuffield Council of Bioethics has advised against its use for this without a medical reason.
It also has the capability to look at the number of sex chromosomes X and Y. An incorrect number of X and Y chromosomes can cause medical problems. However, limited numbers of babies with these conditions (sex chromosome aneuploidies) have been evaluated using NIPT so the accuracy of testing for this is uncertain. Therefore we do not recommend it.
More recently testing for diGeorge syndrome (22q11.2 deletion) has been introduced. The detection rate for this condition is 75%, meaning that 25% of affected babies would be reported as unaffected. Furthermore, the test will wrongly be reported as positive in 1 in 200 women. Again limited numbers of pregnancies have been tested for this so the performance is uncertain. Therefore experts advise against using NIPT for this and we do not offer it as a company. If you are at high chance of having an affected pregnancy with diGeorge syndrome an invasive test (e.g. amniocentesis) is more accurate.
More information:
https://www.tdlpathology.com/specialties/genetics/non-invasive-prenatal-testing-nipt/
Information about the conditions:
Down Syndrome www.downs-syndrome.org.uk
Edward and Patau Syndrome www.soft.org.uk
Turner Syndrome www.tss.org.uk
www.nhs.uk/conditions/turners-syndrome
Klinefelter Syndrome www.nhs.uk/conditions/klinefelters-syndrome
