Chromosome aneuploidies are common genetic defects that can lead to diseases such as Down syndrome. Current methods of aneuploidy testing exist, primarily in the form of chorionic villus sampling or amniocentesis. Although precise, these tests are invasive and may result in intrauterine infection and miscarriage.
Recently, fetal genetic material (found in maternal blood) has been used to screen for fetal aneuploidy in high-risk women. Now a simple blood draw can detect chromosomal abnormalities during pregnancies. However, the limitations of cell-free DNA screening performance can create issues for expecting parents. The failure of cell-free DNA screening ranges from approximately 1% to 8% and varies depending on the laboratory and the methodology used. Receiving a false-positive result can have an emotional toll on expecting parents and can lead to termination of a healthy pregnancy without further testing.
In an article by Strom et. al., published in PLOS ONE, the authors looked into improving the positive predictive value (PPV) of non-invasive prenatal screening (NIPS) assay of fetal aneuploidies by reducing the false-positive rate using massively parallel shotgun sequencing (MPSS) with GC sequence bias corrections.
Maternal mosaicism, undetected tumors, the vanishing twin syndrome, and confined placental mosaicism, as well as technical errors, are possible causes of NIPS false-positive results. However, correct identification of the causes and eliminating the false-positives of NIPS may improve the PPV.
Using MPSS with GC sequence bias corrections, the authors developed a wide separation of Z-score thresholds for affected and unaffected pregnancies. Affected pregnancies had a Z-score >8 and unaffected pregnancies had a Z-score
Unfortunately, the authors report that 10% of the women in the trial that received positive NIPS results for trisomy 21 elected to terminate the pregnancies without confirmation by amniocentesis. They remark that biological and technical issues can still account for false-positive results and that NIPS should remain a screening test only. Additionally, the authors stress the importance for clinicians to advise their patients about the possible errors with NIPS and emphasize further testing using chorionic villus sampling or amniocentesis.
StemExpress is dedicated to accelerating research by providing human blood-derived products to scientists. StemExpress maternal blood samples have been used successfully in the research process to develop blood tests like those mentioned above.
We provide 10mL aliquots of blood from normal or aneuploidy positive pregnancies at varying gestations. Click HERE to see our list of products.