By Clare Murphy
BBC News health reporter
Children are being born with severe genetic abnormalities because their parents are being refused funding to screen their embryos, those working in the field have claimed.
In PGD, a cell is removed and examined for abnormality
Fairer provision of pre-implantation genetic diagnosis (PGD) - in which embryos can be screened for a particular abnormality - could also mean fewer abortions when problems are picked up further down the line, experts from the Assisted Conception Unit at Guy's Hospital say.
The new, fully integrated IVF and PGD centre in London opens on Thursday and will serve couples from across the UK who want to ensure their baby does not carry a potentially life-threatening inherited condition - from cystic fibrosis to some forms of early onset cancer.
But a "postcode lottery" means many parents who would like to use the service cannot necessarily get their local primary care trust to put up the £7,000 needed for the treatment, according to Alison Lashwood, a consultant nurse in genetics and PGD at Guy's.
Funding decisions can take up to a year to be reached, she added.
"There is no doubt that there are couples who go ahead [and conceive naturally] and go on to have further affected children," she said.
In one case known to the centre, a couple who were refused funding despite having lost one child at birth to a severe chromosomal abnormality went on to have two other babies with exactly the same condition.
PGD requires parents to undergo standard in vitro fertilisation (IVF) as usual but at a very early stage, when there are only eight cells in the developing embryo, doctors carefully take one of the cells out to examine the genes.
They then choose the embryos that do not seem to have the genetic fault and implant them in the womb.
While the Human Fertilisation and Embryology Authority has drawn up a list of the conditions for which it is permissible to screen, decisions as to whether to fund this on the NHS are made on a case-by-case basis at a local level.
At present it remains rare - of 13,000 IVF births in 2006, under 50 were babies who had undergone PGD.
Claire Holdcroft is an outreach worker for the Jennifer Trust, which works with families affected by spinal muscular atrophy (SMA) - a neuromuscular disease from which babies can die within the first days of life.
She agreed that some parents did have difficulty obtaining funding for PGD from their local trust, particularly if they already had one child who was not affected by the disease.
"But PGD is not always the best option. It can be a very long and difficult process," she said.
"In my experience if a couple is not opposed to abortion they often prefer to go down the path of natural conception and then undergo testing - if the baby does have SMA they will then think about a termination.
"But for some PGD is the best option, and it would be really helpful if there were nationwide standards for who should be entitled to it so everyone knew where they stood and we knew that, as a national charity, we were giving out relevant advice."
Spectre of eugenics
Josephine Quintavalle, head of the anti-abortion Comment on Reproductive Ethics, said PGD should not be seen as an alternative to abortion as both procedures involved the ultimate destruction of embryos.
"We should not be in the business of making judgements about what is a life worth living and what isn't at any stage of the process," she said, adding that there were couples who would consider simply not reproducing at all if they knew themselves to be carriers of serious abnormality.
But despite the ethical debate, the birth at the start of the year of a baby girl who had been screened and born without the BRCA1 gene - which gives the carrier an 80% chance of developing breast cancer - was widely heralded as an important breakthrough.
Dr Yakoub Khalef, medical director of the Assisted Conception Unit, said any suggestion that PGD was paving the way to a eugenist society of "designer" babies was unfounded.
"We're not doing this on demand, we're doing it solely for serious genetic abnormalities," he said.
And he stressed that the parents who sought this treatment were not after a child with high IQ and sporting prowess.
"At the end of the day, all these people really want is a baby."