Non-Invasive Prenatal Testing
At Sheffield Private Pregnancy Care, we are pleased to announce that we are working in conjunction with TDL Genetics in London to offer a brand new and revolutionary service to our clients – Non-Invasive Prenatal Testing (NIPT). This simple blood test represents the future of screening for chromosomal abnormalities and we are one of the first to offer this service to the women of Sheffield.
What is NIPT?
DNA from the fetus circulates in the mother’s blood. Cell-free DNA (cfDNA) results from the natural breakdown of fetal cells and clears from the maternal system within hours of giving birth. NIPT analyses cfDNA circulating in the pregnant mother’s blood and thus enables prenatal screening for Down syndrome (trisomy 21) and other common fetal chromosomal conditions such as trisomy 18 and 13. NIPT also offers optional testing for the Y chromosome material, which can provide information on fetal sex.
Ariosa Harmony™
The Harmony™ Prenatal Test is used for women with singleton pregnancies of at least 10 weeks’ gestation, including IVF self and non-self pregnancies.
During a pregnancy, cfDNA can be tested to give the most accurate screening approach in estimating the risk of a fetus having a common chromosome condition sometimes called a trisomy. This occurs when there are three copies of a particular chromosome instead of the expected two. The test looks to detect the following trisomies:
- Down Syndrome – Trisomy 21
The most common chromosomal abnormality at the time of birth. It is associated with moderate to severe intellectual disabilities, digestive disease, congenital heart defects and other malformations.
- Trisomy 18 (Edwards syndrome) and Trisomy 13 (Patau syndrome)
These conditions are associated with a high rate of miscarriage. These babies are born with severe brain abnormalities and often have congenital heart defects as well as other birth defects. Most affected individuals die before or soon after birth and very few survive beyond the first year of life.
Risk of NIPT
The testing is non-invasive: it involves taking a blood sample from the mother. The pregnancy is not put at risk of miscarriage, or from other adverse outcomes that are associated with invasive testing procedures such as amniocentesis.
Accuracy
Clinical studies have shown that the Ariosa Harmony™ Prenatal Test has exceptional accuracy for detecting fetal trisomy.
A “high risk” result is indicative of a high risk for a trisomy. The test identifies more than 99% of fetuses with trisomy 21, 98% of fetuses with trisomy 18, and 80% of fetuses with trisomy 13. After the test, the number of women with high-risk results where a CVS or an amniocentesis is strongly recommended is less than 1%.
If the test results show there is a high risk that the fetus has trisomy 21, 18 or 13, it does not mean that the fetus definitely has the conditions, although it is highly likely. For this reason, in the event of a ‘high risk’ (or positive) result, follow-up testing by an invasive procedure is recommended.
In the same way if the test results show that there is a “low risk” that the fetus has trisomy 21, 18 or 13, it is unlikely that the fetus has one of these conditions. However, there is a very small risk that not all trisomy fetuses will be detected.
All results should be interpreted by a clinician. Patients should continue with their usual scan appointments following testing.
Who can have the test?
The test is suitable for any woman who has had an ultrasound scan to confirm that her pregnancy is viable (including all IVF self and non-self donor pregnancies) and that the fetal length is equivalent to a gestation of 10 weeks or more. In IVF cases, the age of the donor should be given to allow an accurate risk score.
The test can now be used in cases of multiple pregnancies, i.e. twins although the test will only give a risk for the whole pregnancy and not an individual fetus. In addition, the test is not valid in the case of a “vanishing twin” where a scan had confirmed a twin pregnancy but then one of the foetuses was found to be non-viable or did not develop past an early gestation
The results will be ready in approximately 5 to 7 working days, at which time most women can have their 12-week scan for a detailed examination of the fetal anatomy, including measurement of nuchal translucency, nasal bone and other important factors. At this visit, patients can discuss the DNA and ultrasound results with their obstetricians and can decide, on the basis of the NIPT result and the ultrasound findings, to have an invasive procedure (for example, CVS or amniocentesis) if they so wish.
Repeat samples
There needs to be enough fetal DNA in the maternal blood to be able to provide a result. If there is insufficient fetal DNA in the sample (occurring in 3% of cases), another blood sample from the mother may be required. This will be processed in the laboratory at no extra charge.
What is the process?
Once you have taken a personal decision that you want to have the non-invasive prenatal test performed, you will be asked to sign a consent form and your blood sample can be taken from a vein in your arm.
Who carries out the analysis of the test?
We will send your blood sample along with your personal information (including name, date of birth, gestational age) to The Doctors Laboratory based in London, who will perform their non-invasive test called Harmony™ Prenatal Test on the DNA extracted from your blood sample.
Can I find out the gender of my baby?
Fetal sex chromosomes Harmony Prenatal Test can also be used to evaluate X and Y sex chromosomes as early as 10 weeks. You have the option to test for conditions caused by having an extra or missing copy of the X or Y chromosomes, including Turner and Klinefelter syndromes (This is only available for singleton pregnancies).
When will my results be available?
The majority of the results are available within 5-7 working days although in a small proportion of cases, additional processing is required which may result in a delay which can be between an extra 3 to 5 days. We are keen to stress that this does NOT necessarily indicate that there is an abnormality in the sample, but rather, the laboratories wish to confirm that their result is as accurate as possible.
Do I need to have any other tests?
NIPT does not replace your 12 week nuchal scan. If you have opted to screen prior to this gestation you are strongly advised to have a scan to check your baby’s anatomy.
NIPT minimises the need for an invasive test but may not replace diagnostic genetic testing such as CVS or amniocentesis in some cases. If you are not reassured by your NIPT screen result the only absolute verification is an invasive diagnostic test but this carries a small risk of miscarriage unlike the Harmony test.
The Ariosa Harmony™ Prenatal Test does not provide information on other rare chromosomal abnormalities. If the ultrasound scan shows a high nuchal translucency or other major physical defects such as brain abnormalities, heart abnormalities, the risk for some rare chromosomal defects may be high. In such cases, you may still choose to have a CVS or an amniocentesis even if the Harmony test has virtually excluded the major commoner chromosomal abnormalities.
The non-invasive prenatal test does not provide information on other physical defects such spina bifida, or information on fetal growth. It is therefore advisable that you have all the usual ultrasound scans during your pregnancy.