NIPT Test : Non Invasive Prenatal Testing For First Trimester Screening
Noninvasive prenatal testing (NIPT) is becoming increasingly popular in the world , with increasing advocacy in the medical community. Most obstetricians now standardly offer cell‐free DNA (cfDNA) to all high‐risk patients . One recent study concluded that cfDNA testing had significantly lower false positive rates and higher positive predictive values for trisomy 21 and 18 than standard screening with serum analytes .
whats the difference ?
As you know the rate of chromosomal anomaly and down syndrome increases with maternal age , thats why always we have to screen all mothers of 35 years old and above to find out if there is any abnormality .
until recent years we were only able to do first trimester screening based on Risk calculations driven from measurement of fetal Nucal translucency in ultrasound and double marker from maternal blood and based on these measurements , the risk was calculate with special analytics .
but what was disadvantage ? this calculations can only show the percentage of risk and most of the time shows false positive results that horrifies patient and family for actually nothing !!!!!
Fortunately ! since 2011
Cell–free fetal DNA testing, also called noninvasive prenatal testing or screening (NIPT or NIPS), became clinically available in the United States as a screening test for fetal aneuploidy (i.e., missing or extra chromosomes, such as in Down syndrome).
in this Year ,Scientists found out that we can find DNA of the fetus circulating in maternal blood vessels and We can easily draw maternal blood and check the fetal DNA in it directly .
one study conducted in finland in 2011, showed that in total 188 case of down syndrome , using standard first trimester screening there was 30 normal cases that were reported falsely positive and there where 34 abnormal cases that was missed and reported false negative .
thats why we recommend using the new Cell free Fetal DNA test called NIPT ,
in one study false negative rate of NIPT for T21 detection was only 0.09%, which is significantly lower than standard first trimester screening test. and false positive is less than 1 percent ,
we can see comparison of these 2 method in the chart below
|Detection rate T21||73%||> 99%|
so with using previous method of screening we will miss 27% of down syndrome cases and we will get 5000 false positive result that only 199 case is really positive , these 5000 cases of false positive will go under amniocentesis procedure ( to get amniotic fluid sample and do genetic test on it ) which is more invasive and costs a lot and takes 4 weeks to get the result .
so why still doctors are ordering standard first trimester screening and not NIPT ?
because its little bit more expensive about double the price of standard test ,
and secondly because most of the time still its not covered by insurance companies .
By : Dr Roya Pourghorban
Specialist OBGYN , Specialist Reproductive Endocrinologist and IVF
Roya Medical center
1. whats the avarage price of the test ?
basic NIPT : 3500 AED
Extended NIPT : 5000 AED
NIPT mostly is done as basic NIPT which detects chromosomes 13, 18, 21, X,Y aneuploidy .
the extended NIPT also can be done to check all 23 pair chromosomes and some of the common microdeletions .
althoough sensetivity of the test is not that high for other chromosomes not same as those 5 chromosomes .