Currently the NHS offers the 1st trimester combined screening test between 11 and 13 weeks and beyond this gestational window a simple quadruple blood test. Both screening tests assess your chance of having a baby with a chromosomal abnormality such as Down’s Syndrome, Edwards’ syndrome or Patau’s syndrome.
An ultrasound scan is used to assess your baby’s growth and well-being, and if the gestational age is between 11 and 13 weeks they will measure the collection of fluid that lies at the back of your baby’s neck, known as the Nuchal Translucency or NT. All babies have this collection of fluid but an increased thickening can be associated with babies affected with chromosomal conditions or certain structural heart conditions.
In the 1st trimester (11 – 13 weeks), the ultrasound measurement of the NT is then combined with a blood test. The blood test assesses the hormone levels of 2 placental blood markers circulating in the maternal blood. Human Chorionic Gonadotrophin (free beta – HCG), and Pregnancy Associated Plasma Protein (PAPP-A). The measurements of the NT and the hormone levels are then combined and a calculation applied to determine the likelihood that you may be carrying a baby with a chromosomal abnormality.
If over 14 weeks then 4 placental hormone blood markers are used to calculate the likelihood.
If the likelihood is greater than 1 in 150, this is classed as “high risk”.
With these tests, it is important to note the following:
- As many as 1 in 30 pregnant women may be given a high-risk result.
- These women will be then offered the option of an invasive test such as amniocentesis or chorionic villus biopsy (CVS) to assess their baby’s chromosome pattern.
- The possibility of miscarriage from this test is approximately 1%.
- Nearly all women who are offered an invasive test will be carrying a normal healthy baby!
- The test will only identify 60 – 80 % of affected babies
- The test will NOT identify 20 – 40% of affected babies
Move over Fate…. Let Next Generation Sequencing take the lead….!
***There is a NEW accurate alternative which is simple, safe and risk free***
Non-invasive prenatal testing (NIPT): available from 10 weeks
NIPT is a new generation of advanced screening for chromosomal abnormalities and can be used from as early as 10 weeks. Ultrasound is still used to assess the baby and again we obtain a simple maternal blood sample but then science steps in.
Next Generation Sequencing takes the maternal blood sample and extracts fragments of free floating placental DNA (cfDNA) which is of the same or comparable make-up to your baby’s DNA. These fragments are then analysed to assess the likelihood of your baby having a chromosomal abnormality.
With this test:
- Fewer than 1 in 1000 pregnant women will be given a high-risk result
- Only women with a positive result will be then offered an invasive test such as amniocentesis or chorionic villus biopsy (CVS) to confirm or rule out the NIPT analysis.
- This reduces significantly the number of women put at risk of miscarriage from the invasive test.
- Nearly all women who are offered an invasive test will be carrying an affected baby
- The test will identify 99.9% of affected babies
- The test will NOT identify 0.1% affected babies
At this is my: baby not only will we perform an ultrasound scan to assess your baby’s growth and well-being, we also give you the added reassurance of a structural check of your baby’s anatomy. This includes a check of the standard ultrasound markers for the potential increased risk of your baby having a chromosomal problem. On the whole, this scan will provide early reassurance that all looks well structurally and that potentially your pregnancy is low risk for a chromosomal abnormality whilst you wait for the NIPT result. NIPT is far more accurate than ultrasound alone for assessing the risk of a chromosomal abnormality.
Advantages of NIPT:
- The BEST detection rate of all screening tests.
- 100% safe for you and your baby.
- Greater than 99% accurate
- Can be done from as early as 10 weeks
- Less than 1 in 3000 women will be given a false positive screen result
- Available to all women including Twins and IVF pregnancies.
- Option of gender information (See below).
Additional screening options:
Most NIPT screens will offer analysis of the X and Y sex chromosomes. In singleton pregnancies, it will identify the possible gender of your baby (accuracy >98%). In twin pregnancies, it will check for the presence of the Y chromosome, this will tell you that at least one of the babies you are expecting is likely to be male. We always advise to have the gender checked at your 20 week ultrasound anomaly scan. The assessment of your baby’s gender is entirely optional.
Since NIPT can identify X & Y chromosomes, most screens will offer you the option to screen for the risk of sex aneuploidy conditions including Turner’s (Monosomy X), Klinefelters (XXY), Triple-X (XXX) and Karyotype XXY. The screening for sex aneuploidy conditions is not common practice; it requires appropriate counselling and is an option.
With new advancements in screening, testing for all chromosome and some micro-deletion abnormalities is possible. Again, this is optional and can incur an additional charge. Screening for these conditions is not common practice and again requires appropriate counselling.
Limitations of NIPT:
NIPT testing alone does not provide information on physical defects, mosaicism, partial trisomy, or translocations and thus it is essential that a detailed ultrasound scan is undertaken for full evaluation purposes.
NIPT testing with any provider is dependent on the amount of cfDNA circulating within it, and sometimes there is not enough. In these cases, the result can be delayed as further analysis is needed and in some cases another blood sample or redraw would be required.
Blood samples are usually dispatched the next working day after the sample draw.
If you have recently undergone a blood transfusion, transplant surgery, immunotherapy, stem cell therapy or anti-coagulant therapy please speak with an advisor at this is my: baby prior to the blood sample being taken.
Turnaround Time (TAT) is estimated when the sample reaches the laboratory in working days (NOT calendar days). 95% of samples will have a result within this time scale, but when further sequencing is needed in order to obtain a result, TAT can be slightly longer.