This form of pre-implantation chromosomal analysis should not be confused with preimplantation genetic diagnosis (testing of embryos to determine whether they will be affected by a specific serious genetic disorder, typically due to family history of that disease), nor with Counsyl’s ‘universal’ preconceptual genetic test, which screens prospective parents to see whether are carriers for a large number of different genetic disorders of varying severity (see previous news).
A new genetic technique to screen embryos produced by in vitro fertilisation (IVF) has been hailed as a potential advance. The test, called 24sure, analyses chromosome number using then polar body from the fertilised egg cell (ooctye); abnormal numbers of chromosomes (aneuploidy) is thought to be a leading cause of early miscarriage. This is a significant problem for IVF, especially as aneuploidy rates are higher in older women. The less severe forms of aneuploidy may not result in pregnancy loss, but nevertheless cause significant fetal abnormality.
A small scale study by the European Society of Human Reproduction and Embryology (ESHRE) preimplantation genetic screening (PGS) task force found the test could identify aneuploidy (abnormal chromosome number) in 89% of fertilised eggs within 12 hours, fast enough to make normal implantation feasible (see press release).
PGS Task Force coordinator Professor Geraedts commented: “With chromosome errors being the predominant cause of non-viability of the embryo, we hope this approach will in future effectively improve results in assisted reproduction”. However, there is not yet any evidence to show that such testing actually does improve pregnancy and birth rates among IVF patients, with more trials required (see BBC news).