by Dr. Francisco M. Gil-Salas
PhD, MSc, B. Pharm
An essential step in providing security, prenatal testing ensures that you stay informed about the status of your pregnancy. Aside from reducing anxieties and stress, it gives you peace of mind and also an expectation of what’s in store for the journey ahead, so that you are able to provide the best start for your child.
The detection rates of conventional screening tests currently available vary from less than 70% to a high of 84%, implying that 16% to 30% abnormal fetuses are potentially missed during screening. In addition, the false positive rate of 5% in these traditional screening techniques means that 1 in 20 women undergoing screening will be subjected to an unnecessary invasive test.
Since the groundbreaking discovery of cell-free DNA (cfDNA) in maternal circulation in 1997, it has opened up new possibilities for non invasive prenatal testing (NIPT). NIPT has been increasingly used as a screening test to detect fetal chromosome abnormalities. It analyses cell-free DNA present in maternal blood, using the cutting-edge Next Generation Sequencing (NGS) technology. This cfDNA comes from the placenta and circulates freely in the maternal bloodstream. Millions of reads of sequencing data from this cfDNA are analysed to detect the risk of aneuploidies, such as Down Syndrome with accuracy of up to 99%.
Whole Genome Sequencing approach based NIPT, such as iGene®, provides comprehensive coverage for chromosome abnormalities. Such test can be performed as early as 10 weeks of gestation, although waiting till 12 weeks is recommended when the pregnancy is more stable. It could be viewed as complementary to first trimester ultrasound evaluation and nuchal translucency assessment (NT Scan). Expectant mothers include women with anyone of the following conditions may consider iGene®:
- Advanced maternal age (Over 35)
- Abnormal maternal serum screen
- Abnormal ultrasound findings suggestive of fetal trisomy
- High and intermediate Risk” in First Trimester Screen
- Family history of chromosomal abnormalities
NIPT like iGene® is a highly accurate screening test, however it is not a diagnostic test. It does not test for all chromosomal conditions. Therefore, a “screen negative” result does not completely rule out all fetal chromosomal disorders that were not tested. Confirmatory testing, appropriate follow-up obstetric care and counseling are strongly recommended for who are identified as being at high or elevated risk.
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