The embryos were frozen 12 years ago

The boy and girl, who are healthy, were born nine months ago to their 39-year-old mother.

The woman already has another set of twins, now 12, from the same batch of embryos.

Doctors said it was the first successful implantation of embryos frozen for so long.

I don't think there are any medical risks in relation to the length of time the embryos are frozen for Dr Mohammed Taranissi, Assisted Fertility and Gynaecology Centre

Doctor Ariel Revel of the Hadassah Hospital's IVF unit, said: "This is the longest recorded time.

"The implication is that the length of time that embryos are frozen is not crucial and probably there is no more damage happening during the many years they are frozen."

The previous record is thought to be seven years.

Ethical questions

Dr Revel said the fact babies had been born successfully after the implantation of such old embryos could raise ethical questions in the future if women asked to be impregnated with embryos frozen decades before.

He added: "Maybe we could see patients coming back to us at an older age, and then it raises all sorts of ethical and social questions."

The Human Fertilisation and Embryology Authority said embryos in Britain were stored for five years, but could be stored for an extra five years if a doctor confirms the couple have significant fertility problems.

A spokeswoman said: "In exceptional circumstances you can extend longer than 10 years, but to do that two doctors need to confirm that the couple have or will become prematurely infertile."

Dr Mohammed Taranissi, of London's Assisted Fertility and Gynaecology Centre, told BBC News Online: "I don't think there are any medical risks in relation to the length of time the embryos are frozen for.