18 January 2016
Ghent University; Academic Medical Centre, Amsterdam; Maastricht University, the NetherlandsAppeared in BioNews 835
Under the auspices of the Virtual Academy of Genetics, COGEN (Controversies in Preconception, Preimplantation and Prenatal Genetic Diagnosis) recently issued a 'consensus statement' on preimplantation genetic screening (PGS), based on a scientific meeting held in Paris last September.
The goal of PGS is to screen out aneuploid embryos and only transfer those identified as chromosomally normal during IVF. Although the scientific rationale makes sense to a certain extent, previous versions of PGS were found to decrease pregnancy rates considerably following its use in clinics around the world for several years (1).
Nevertheless, many have high hopes for a PGS revival with new screening methods. As there was a lively debate on the merits of this 'new PGS' at the meeting (and a clearly divided opinion in the room at the end of the debate), one would expect the consensus statement to reflect this.
For example, the consensus might have been that PGS seems to be a promising technology for women who suffer psychologically from repeated miscarriages or for women who want to have the shortest time to pregnancy possible. But, with the caveat that more data are needed to confirm if, and for which patients, PGS might be useful (the three currently available RCTs, randomised controlled trials, have obvious shortcomings ). We must also bear in mind that some embryos that are reported as aneuploid do result in a healthy live birth (3).
Carefully informing the patient of those uncertainties is crucial. This is extremely important when it comes to PGS, as a meta-analysis of all trials conducted on the efficacy of the first versions of PGS demonstrated a decrease in live birth rate per cycle commenced (1). This fact might be too obvious to state for scientists in the field (how could success rates per started cycle ever increase by discarding embryos?), but it is far from clear in much of the information distributed to the lay public.
Alas, everything after the 'but' cannot be found in the 'consensus' statement – a missed opportunity, in our opinion. The statement reads more like a one-sided sales talk, boosting the (alleged) benefits of PGS and either downplaying or completely ignoring the concerns that were raised during the debate in Paris and in the literature (2,4,5). At the same time, issues that are not necessarily related to PGS, such as the benefits of single embryo transfer (which should be the norm in any case), and drop-out rates were included.
The 'consensus' statement reads: 'PGS should no longer to be considered an experimental procedure ... and, where possible, should be made available for routine practice.' They write: 'We therefore believe that PGS should be part of the discussion with all patients considering/undergoing IVF treatment' [our emphasis]. Several of the eminent scientists who signed the statement disclose ties to commercial companies and at least six openly promote PGS on the Illumina website (the company selling PGS), which at least hints at possible conflicts of interest.
The irony of the matter is that, although the data are currently lacking, it might be that future data will show that PGS can reduce miscarriage rates and reduce time-to-pregnancy. Perhaps future data might even show that specific patient populations have a higher chance of having a baby thanks to PGS (namely, those who cannot afford to lose time on multiple transfer cycles that are bound to fail because their reproductive potential is decreasing fast).
So why is the offering company's focus on increasing IVF success rates (by which they really mean, but do not say, increased implantation rates per embryo transfer) and not on reducing miscarriage rates and time to pregnancy? Maybe they realise that, in the eyes of most patients, success really means going home with a baby. The truth about PGS is that it does not increase – but decreases – the chance of this happening and perhaps that reality doesn't sell quite so well.