Preimplantation genetic screening (PGS) for aneuploidy is a powerful genetic test that may be performed on embryos during IVF treatment to screen for numerical chromosomal abnormalities. PGS is performed on a small embryo biopsy prior to transfer and identifies which embryos are chromosomally normal.
Webinar on PGS Testing
The Harmony test (Ariosa Diagnostics, California USA) is a type of non-invasive prenatal test (NIPT). The Harmony test assesses blood from the mother, looking at the baby’s DNA in her blood (analyses maternal serum for fetal DNA).
It provides limited screening for chromosomes 21, 13, 18 and/or XY (sex chromosomes).
The Harmony test has a higher detection rate for trisomy 21 than combined first trimester screening (nuchal translucency scan plus maternal serum screening).
The Harmony test identifies:
- 99% of the fetuses with trisomy 21 (Down syndrome)
- 97% of fetuses with trisomy 18 (Edwards syndrome)
- 92% of fetuses with trisomy 13 (Patau syndrome)
The Harmony test, and all other forms of NIPT, is an advanced screening test rather than a diagnostic test. It does not detect all cases of trisomy 21, 18 or 13.
It can be performed after 10 weeks of gestation. It can be performed in single, twin and IVF pregnancies.
As early as nine weeks into your pregnancy, a simple blood draw can tell you if your baby is at higher risk for having Down syndrome and other common genetic conditions, as well as the gender of your baby. Non-invasive and highly accurate, Panorama identifies more than 99% of pregnancies affected with Down syndrome and has the lowest reported false positive rate of any prenatal screening test for the commonly screened chromosomal abnormalities: trisomy 21, trisomy 18, and trisomy 13.
Nuchal scan (NT procedure) is performed between 11 and 14 weeks of gestation, because the accuracy is best in this period. The scan is obtained with the fetus in sagittal section and a neutral position of the fetal head (neither hyperflexed nor extended, either of which can influence the nuchal translucency thickness). The fetal image is enlarged to fill 75% of the screen, and the maximum thickness is measured, from leading edge to leading edge. It is important to distinguish the nuchal lucency from the underlying amniotic membrane.
Normal thickness depends on the crown-rump length (CRL) of the fetus. Among those fetuses whose nuchal translucency exceeds the normal values, there is a relatively high risk of significant abnormality.