LONDON (AP) -- Experts called Tuesday for an investigation of Britain's in-vitro fertilization program after reports that a white couple who underwent the procedure had black twins.

"There are obviously problems with the transplant of embryos and eggs, there is no doubt about that," said Tim Hegley, director of the Electronic Infertility Network - a nonprofit organization providing information about infertility.

"People undergoing IVF are very worried by this."

According to media reports, the white couple had tried unsuccessfully for years to have a child and went to a fertility clinic for IVF treatment.

In that process, sperm and egg are joined in a laboratory and the resulting embryo is implanted in the womb.

The Sun newspaper, which broke the story Monday, said the white mother wanted to keep the children. The case has attracted widespread coverage in the British media, despite a court injunction protecting the identities of all parties, including the clinic, and details of the fertility treatment they underwent.

Fertility experts said Tuesday that other mix-ups may have occurred in the past.

"This only came to light because the children were black and the parents were white," said Hegley. "I suspect this could be more widespread. People undergoing IVF have phoned me and asked, 'How can I know for sure they are my children?' It is worrying."

The Human Fertilization and Embryology Authority - the government-appointed body which licenses and inspects fertility clinics - said stringent procedures were in place to prevent mix-ups.

"People using infertility services in the U.K. can be confident that the clinics they attend are regulated more closely than anywhere else in the world," said director of communications Ann Furedi.

"Of course, no system can be guaranteed to be 100 percent fail-safe. There is always the possibility of human error," she added.

Lynn Fraser, professor of reproductive biology at King's College London, said clinics were extremely careful and ensured that all the important stages of the IVF procedure were witnessed by two people.

"The procedures are there, and if they are followed absolutely rigorously one would not expect the system to fail," she said. "But people who carry out these procedures are human."

The government health department, asked to comment on the report, only provided a copy of the injunction, a document stating that claims are before the High Court concerning fertility treatment given to a woman identified as Mrs. A and the biological parentage of children identified as YA and ZA. The preliminary hearing is set for Oct. 10.

According to The Sun, the couple was dismayed the twins were black but were determined to keep the babies.

Mohamed Taranissi, director of the Assisted Reproduction and Gynecology Center in London, said about 40,000 cycles of IVF treatment are conducted in Britain each year. "To my knowledge, it is the first time this has happened in the U.K. It is a very, very rare event," he said.

In 1998, New Yorker Donna Fasano gave birth to twins - one black, one white - after the wrong embryo was implanted in her womb.

The white child was her biological son; the black child was no relation, and his biological parents won custody of the infant.

Copyright 2002 The Associated Press. All rights reserved.