Fertility clinics are extremely unhappy about having to destroy the frozen embryos, which have a potential for life. Implanted in a woman's womb, a proportion of them would develop into babies without further medical intervention.
But frantic last-minute attempts to contact the parents, who have the power to prevent destruction, have largely proved fruitless. Hundreds of letters have been sent out, but most have produced no response.
Concern about the scale and implications of the destruction is growing, and anti-abortion activists have suggested that where parents cannot be found, the embryos could be put up for adoption.
Clinics are particularly concerned. "The thought of having to dispose of these embryos is not a happy one," said Peter Brinsden, medical director of Bourn Hill, Cambridgeshire, which is going to have to dispose of about 500 embryos.
"But we now feel the couples for whom we froze them, have given up on them. It would be unethical to allow children to be conceived from these embryos without the consent of the couples who produced them, or for them to be used for research."
Many are worried that couples will reappear, hoping to use their frozen embryos. "I am certain that some will come back in future and we will have to say: 'Sorry, we tried to contact you, but were unable to do so'," said Dr Robert Forman, clinical director of the London Gynaecology and Fertility Centre.
Many couples may be unaware that they can extend the five-year storage period by another five years.
The Human Fertilisation and Embryology Act, which came into effect on 1 August 1991, laid down a maximum storage period of five years, but new regulations which came into effect in May, said that the period could be extended, with the written consent of the parents.
The freezing of embryos began in 1983, because in-vitro fertilisation treatment usually produces more embryos than can be replaced in the womb. The spare embryos are stored in liquid nitrogen.
The scale of the impending destruction has not hitherto been recognised. Last summer, 52,000 embryos were in storage, of which 9,000 were frozen before August 1991. The Human Fertilisation and Embryology Authority (HFEA) hopes that only 1,000 of this 9,000 will remain unclaimed by the 31 July deadline, the rest either having been used by couples for their own treatment or having been given away or destroyed, according to the couples' wishes.
But Independent on Sunday inquiries suggest that that estimate is too low. The total still unclaimed at six of the biggest clinics is almost 2,500, and there are another 25 clinics involved.
Two pressure groups, Comment on Reproductive Ethics (Core) and the anti- abortion organisation Life, would like to see the embryos put up for adoption. "To adopt an abandoned embryo is not that unusual," said Josephine Quintavalle of Core. "Donating these embryos to infertile couples would be to give them the possibility of life, though it could have to go hand in hand with a ban on embryo freezing, so that the problem does not arise again."
But Ruth Deech, chairman of the HFEA, dismissed the idea of adoption without parental consent as "unacceptable".
"It would not be appropriate to either human dignity or the autonomy of the individual to give these embryos away or use them for research without the informed consent of the parents," she said.
"I would not regard letting them perish as a waste of human life as Life does, because an embryo is not a little baby in the freezer. They are less than the size of a full stop. One must remember that, in nature, every month, without women even realising it, thousands of embryos are lost. The majority do not implant. You could say that by freezing embryos, we are preserving more lives than would be preserved in nature.
"Many embryos do not survive the thawing process, or thaw and are seen not to be very good quality, or thaw and will not implant. The success rate of IVF using thawed embryos is less than that using fresh ones - 12.7 per cent compared to 14.7 per cent - so most of them would not implant anyway."
Mrs Deech added that the demand for embryos among infertile couples was much less than that for donated eggs or donated sperm. Most couples seeking treatment wanted a child that was as much genetically theirs as possible, and it was unusual for couples not to be able to use either their own sperm or their own eggs.Reuse content