One drop for peace of mind
Down's syndrome, cystic fibrosis, thalassemia: these are just three of the genetic disorders that strike a note of fear with parents-to-be, especially if the mother is in her mid to late 30s or there is a history of foetal abnormalities in the family.
At conception, 23 chromosomes are passed from each parent to the embryo. The correct number of chromosomes that cells/embryos should have is 46. However, there is a statistical chance that one chromosome will be missing or that one extra chromosome is present. When this happens, it is termed foetal aneuploidy. Depending on the chromosomal abnormality, foetal loss, developmental and speech delays, growth delays, and sexual characteristics may fail to develop. Down syndrome is an example where an extra copy of chromosome 21 is present.
Women aged 35 plus or with a family history of foetal abnormalities have a higher statistical risk of foetal aneuploidy (as high as 1 in 160 births). Although certain groups of women are at a higher risk, all women should have access to screening for fetal chromosomal abnormalities.
Conventional screening methods have used both ultrasound and serum markers (with a blood sample taken from the mother) to determine the presence of fetal abnormalities. However, depending on which combination of screening methods is used, a five to 35-per-cent chance of missing a diagnosis and a five-per-cent chance of a false positive result exists. Women who test positive are then offered amniocentesis or chorionic villus sampling to confirm the diagnosis. Both amniocentesis and chorionic villus sampling are considered invasive tests carrying a 0.5-per-cent risk of foetal loss.
The Non-Invasive Foetal Trisomy (NIFTY) test is a relatively new and advanced screening tool. It uses a 6ml sample of blood from the mother and analyses the foetal free cell DNA. In addition to screening for Down syndrome, the NIFTY test also screens for Edward syndrome (chromosome 18), Patau syndrome (chromosome 13). However, the NIFTY test is not used to detect foetal sex.
The benefits of the NIFTY test include a much higher detection rate (more than 99 per cent for autosomal abnormalities such as Down syndrome) and a much lower false positive rate (less than one per cent). With a much lower false positive rate, women can avoid the need for confirmatory invasive testing, such as amniocentesis and chorionic villus sampling, and their corresponding risk of foetal loss.
The blood sample can be collected any time after 12 weeks gestation as opposed to conventional screening methods that necessitate multiple ultrasounds and blood samples taken at specific weeks of gestation. Furthermore, results are available sooner, with most women informed of their test results within three weeks time.
In comparison to conventional methods the NIFTY test is more reliable, simple to do, safe for the mother and foetus, and the results are delivered in a timely manner, thereby, providing parents with peace of mind or allowing for prompt access to genetic counselling sooner than previously possible.
If you are pregnant, consider asking your health care provider if the NIFTY test is available.
Dr Boonsaeng Wutthiphan is a specialist in Infertility & Gynecologic Laparoscopic and Hysteroscopic Surgery at Samitivej Sukhumvit Hospital. Call the Women’s Health Centre at (02) 711 8181 or email: [email protected].
