By Michelle Roberts
BBC News, Health reporter in Lyon
An expensive treatment designed to improve a woman's chance of pregnancy actually does the reverse, Dutch research suggests.
Embryos are screened for defects
Preimplantation genetic screening (PGS) checks embryos for abnormalities so the best ones can be implanted.
A fertility conference in Lyon heard women who used PGS were nearly a third less likely to get pregnant than those who opted for conventional IVF.
Experts said women desperate for a baby were being exploited financially.
The pioneer of PGS, Professor Alan Handyside, defended its use in high risk women.
The work, published in the New England Journal of Medicine, looked at 408 women aged 35-41 - a typical age range for PGS use.
Sebastiaan Mastenbroek's team from the Centre for Reproductive Medicine at the University of Amsterdam compared three cycles of IVF with and without PGS in 408 women.
At 12 weeks, 74 or 37% of the IVF group was pregnant compared with just 52 or 25% of the PGS women.
The PGS women also had a significantly lower live birth rate - 49 or 24% compared with 71 or 35% with IVF.
Damage to embryo
Mr Mastenbroek offered several reasons for why this might be, and plans further work to test these theories.
"Perhaps the biopsy of one cell that is needed for PGS is more damaging to the embryo than is thought at the moment.
"Or the cell biopsied may not represent what is going on in the rest of the embryo.
"It is not possible to look at every chromosome in PGS, so maybe there are still abnormal chromosomes that we cannot see." He said PGS should not be used routinely in patients.
"Until this technology has been proven it should be kept in the research setting," he said.
Professor Handyside of the London Bridge Fertility, Gynaecology and Genetics Centre said: "We advocate that we target these testing to those couples that we do know are at risk of abnormalities.
"Our worry is that women who are genuinely at risk will be put off having this treatment which can be of benefit to them."
He said in the future it should be possible to screen for all 23 pairs of chromosomes with PGS and reduce the cost of the procedure.
British Fertility Society spokesman Mr Stuart Lavery said: "We need to approach the use of PGS with caution. It should not be offered routinely.
"But there are patients for whom PGS might be considered - such as patients who routinely produce good numbers of apparently healthy embryos that never achieve implantation when they are transferred into the uterus."
Professor Peter Braude, of Kings College London, said: "Vulnerable patients should no longer be exploited financially under the impression that it works.
"A similar study should be undertaken for PGS use in repeated IVF failure and recurrent miscarriage - other techniques in which it is purported to work."
Alison Murdoch, Professor Of Reproductive Medicine, Newcastle Fertility Centre At Life, said: "Patients who pay for PGS as part of their IVF treatment should be made aware of these results."
Of the 40,000 IVF cycles carried out in the UK in 2004, 103 included PGS.
PGS typically costs £1,300 for a five chromosome screen and £1,700 for a seven chromosome screen in the UK.