At conception twenty-three 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 will be present. When this happens it is termed fetal aneuploidy. Depending on the chromosomal abnormality fetal loss, developmental and speech delays, growth delays, and sexual characteristics may fail to develop. Down syndrome is an example of when an extra copy of chromosome 21 is present.
Women with a family history of fetal abnormalities and those over the age of 35 years, have a higher statistical risk of fetal 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 (when 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 5-35 percent chance of missing a diagnosis and a five percent 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 percent risk of fetal loss.
The Non-Invasive Fetal Trisomy (NIFTY) test is a relatively new and advanced screening tool. It uses a 6 ml sample of blood from the mother and analyses the fetal 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 fetal sex.
The benefits of the NIFTY test include a much higher detection rate (> 99% for autosomal abnormalities such as Down syndrome) and a much lower false positive rate (< 1%). 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 fetal 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 perform, safe for the mother and fetus, and the results are delivered in a timely manner. Thereby, providing parents with peace of mind or allowing for access to genetic counseling sooner than what was previously possible.
If you’re pregnant consider asking your health care provider if the NIFTY test is available. Samitivej Hospital has the technical capacity to carry out the NIFTY test and Samitivej Hospitals’ treating physicians welcome any questions that you may have regarding pregnancy and fetal abnormality screening.
M.D., Faculty of Medicine, Prince of Songkla University Faculty of Medicine Prince of Songkla University , 1979