28 Jan PGS testing during IVF: should you have it?
Preimplantation genetic screening, or PGS, is a viable option for certain IVF patients. Available, for an additional fee, to IVF couples anxious about the chromosomal health of their embryos, PGS takes place before your embryo transfer (and delays it until the results are back). Due to its pre-transfer timing, it has to be better than chorionic villus sampling or an amniocentesis, which look for fetal problems several weeks into a pregnancy.
PGS’s trump card is that screening for genetic problems before embryo transfer empowers IVF couples. They can make an informed choice, based primarily on maternal age, miscarriage history, past IVF treatment outcomes and their clinic’s advice, on whether to have PGS or not. The results don’t lie: a PGS-tested embryo either has normal chromosomes or it doesn’t.
So how does PGS work? Trophectoderm cells (the ones that form the placenta) are biopsied, via a man-made hole in the embryo’s shell, on day five or six of an IVF cycle. The PGS-tested embryo is then vitrified and the sample sent to the lab. Using a process called NGS (next generation screening), the cells are checked for chromosomal irregularities (e.g. Down’s syndrome). Only healthy embryos are transferred in a later frozen embryo transfer, potentially improving the chance of successful treatment.
PGS is also known as aneuploidy screening, or PGT-A. It looks solely as the chromosomes and doesn’t identify specific genetic conditions (PGD does that). Past embryo-screening techniques took biopsies on day three, and weren’t that great. But some embryos don’t make it to day five, so PGS can be cancelled. Biopsied embryos may also implant less easily than non-tested embryos. But the low risk of that happening is offset by the benefits of transferring a healthy embryo.
PGS isn’t perfect. It can’t guarantee future IVF treatment will succeed, despite ruling out many chromosomal anomalies and giving an embryo the genetic green light. There’s also a 5% margin of error: certain chromosomal problems slip through the net. Research on the benefits of PGS is inconclusive. So patients really do need to be guided by their clinics carefully. Additional prenatal screening should not be ruled out.
The majority of aneuploid embryos are due to extra or missing chromosomes in the egg. Sperm cells are only to blame in 10% of cases. Perhaps the key reason for considering PGS is advanced maternal age: if you’re over 35, chromosomally abnormal eggs are more common. Miscarriage history comes second. And past failed IVF cycles come third. But your doctor will advise.
The ultimate benefit of PGS is that IVF patients who have it, and go on to transfer chromosomally normal embryos, may get pregnant quicker and need fewer IVF cycles in the future. This reduces distress and saves money. Although PGS can’t ensure a live birth on its own, it gives couples a degree of confidence and control. For that, many will be prepared to pay for it.