Screening Embryos Before IVF Implantation Leads To Fewer Babies For Older Women, New Study

Preimplantation genetic screening (PGS) fails to improve IVF outcomes in older women; it leads to fewer pregnancies and live births, an embryologist from
The Netherlands announced at the 23rd annual conference of the European Society of Human Reproduction and Embryology (ESHRE) in Lyon, France,
yesterday.


The findings of the study are also published in the New England Journal of Medicine (NEJM).


Pregnancy rates of older women having IVF tend to be disappointingly low, wrote the researchers, and there is a view that screening embryos
before implantation for problems such as aneuploidies (too few or too many chromosomes) is a way to improve the effectiveness of IVF for these women.


Sebastiaan Mastenbroek,from the Centre for Reproductive Medicine of the Academic Medical Centre of the University of Amsterdam, and his team tested this
hypothesis and concluded that PGS should not be carried out routinely on embryos that are to be implanted in women over 35.


Mastenbroek and colleagues conducted a multi-centre, randomized, double-blind, controlled trial where they compared three cycles of IVF with and without PGS
in 408 women aged between 35 and 41.


206 of the women were assigned to PGS, while the rest were not (non-PGS, or control group).


The ongoing pregnancy rate was considerably lower in the PGS group compared to the non-PGS group.


Mastenbroek said:


"We found that, at 12 weeks, 52 of the women in the PGS group were pregnant (25 per cent), whereas 74 of the control group (37 per cent) had an ongoing
pregnancy."


"And the women in the PGS group also had a significantly lower live birth rate: 49 or 24 per cent, as opposed to 71 or 35 per cent, of the controls," he
added.


The researchers concluded that:


"Preimplantation genetic screening did not increase but instead significantly reduced the rates of ongoing pregnancies and live births after IVF in women of
advanced maternal age."


Speculating on their findings, the researchers said there could be several explanations for the failure of PGS to improve IVF in older women.


Perhaps it's the biposy of a cell from an early embryo (this is taken on day 3 after conception) that hampers successful implantation, said Mastenbroek,
although the effect of biopsy alone has not yet been studied.


Also, there is a limit to the number of chromosomes that can be tested by PGS and that could lead to implantation of embryos that appear normal but are not.
For instance IVF often produces mosaic embryos (more than one genetic individual), so testing a single cell does not analyse chromosomes representative of
all the cells of the embryo.


Many IVF centres worldwide are using PGS more and more. In 2003 the ESHRE preimplantation genetic diagnosis (ESHRE-PGD) consortium received reports of more
than 1,700 IVF cycles for which PGS were used. Since only 50 per cent of the IVF centres in the world report their data to the consortium, this figure is
likely to be an under-estimate, said the researchers.















Talking about figures for the US, Mastenbroek said that:


"In a recent survey of 415 assisted reproductive technology clinics in the US, 186 respondents (45 per cent) reported that they had performed a total of
2,197 cycles of PGS in 2005."


Mastenbroek and colleagues are going on to study why PGS does not work. Even though there is no scientific evidence to support the effectiveness or otherwise of PGS
apart from this study, patients and doctors are inclined to use it.


"The idea of screening embryos for chromosomal abnormalities to increase live birth rates in IVF is very plausible, and women of advanced maternal age are
willing to undergo any technique that may provide them with a baby," Mastenbroek explained.


He also said that more studies are needed since their research only covered older women who have PGS:


"We believe our findings imply that the efficacy of the technique also needs to be investigated in other groups of women who are offered PGS, such as those
who suffer recurrent miscarriage or repeated failure of IVF, since evidence for a benefit of PGS in these groups of women is currently still
lacking."


"In Vitro Fertilization with Preimplantation Genetic Screening."

Mastenbroek, Sebastiaan, Twisk, Moniek, van Echten-Arends, Jannie, Sikkema-Raddatz, Birgit, Korevaar, Johanna C., Verhoeve, Harold R., Vogel, Niels E.A.,
Arts, Eus G.J.M., de Vries, Jan W.A., Bossuyt, Patrick M., Buys, Charles H.C.M., Heineman, Maas Jan, Repping, Sjoerd, van der Veen, Fulco.

N Engl J Med 2007 357: 9-17

Volume 357:9-17, July 5, 2007, Number 1


Click here for Abstract.


Click here for more information on Assisted Reproductive Technology (from the
CDC).


: Catharine Paddock

Writer: blog