The Prenatalis® Test is an accredited and highly accurate method to detect the most common trisomies (21, 18, 13) and gonosomal aberrations. However, chromosomal structural changes, translocations or mutations in single genes are not included in the screen. Despite its high sensitivity and specificity, false-positive and false- negative results may occur. The test result describes a risk value rather than a diagnosis.
All commercial NIPTs require an adequate fraction of fetal DNA which should not fall below 2.7% of total cell-free DNA. If the cell-free DNA concentration is too low, a result might not be obtained. In these very rare instances another blood sample will be required.
Possible Reasons for a Second Blood Sample
- low fraction of fetal DNA caused by e.g. maternal weight (> 80 kg)
- long shipping time of the blood sample (> 5 days)
- complex case constellations
Twin Pregnancy and Gender
The presence or the lack of an Y chromosome can be determined in women expecting twins. However, a valid statement on gonosomal aneuploidies such as Monosomy X, XXX, XXY, XYY cannot be made. Neither is it possible to determine which of the two fetuses is affected.