A Spanish woman who became the world's oldest mother at the age of 66 has died of cancer just two-and-a-half years after giving birth to twins, raising fresh questions about the ethics of fertility treatment for women past natural childbearing age.

Maria del Carmen Bousada, a single mother and retired sales assistant from Cádiz, southern Spain, leaves behind her orphan sons, Pau and Christian. It was unclear who would look after them.

Bousada, who had reportedly been diagnosed with a tumour just a few months after the birth in December 2006, had been living with her sons in a one-bedroom apartment and was being helped by her brother and sister-in-law, who are both in their 70s. They lived off the €600 (£515) she received for her pension and from child benefit payments. Her brother, Ricardo Bousada, reportedly said he had sold the rights to her story to a television company and that the proceeds would go towards raising the children.

Bousada became pregnant after repeated visits to a fertility clinic in Los Angeles, where she lied about her age. She told the Pacific Fertility Clinic that she was 55, the cut-off age. Bousada sold her apartment to pay for the treatment, which she did not start until her own mother, for whom she cared, had died.

An 18-year-old girl provided the egg and an Italian-American sperm donor provided the sperm so that, after hormone treatment to reverse menopause, an embryo could be implanted in her uterus.

"I picked them from photos in a catalogue," she said of the donors. "It was a bit like studying an estate agent's brochure and choosing a house."

After a difficult pregnancy the twins were born by caesarean section at a clinic in Barcelona, eastern Spain, a week before her 67th birthday. Shortly after giving birth Bousada told the News of the World that she hoped to live until she was 101, like her mother. "Everyone has to have children at the right time for them. This was the right time for me. It was something I always dreamed of," she said.

"No one at home knew what I was doing," she added. "I told a few girlfriends that I loved the idea of having a baby, but none of them took me seriously. They thought it was impossible."

The clinic's director, Vicken Sahakian, had already expressed disappointment that Bousada falsified records. He said: "I figured something might happen and wind up being a disaster for these kids, and unfortunately I was right."

Regulations for IVF vary greatly around the world and even within Europe, despite EU measures to unify safety standards for donated eggs and sperm. In the UK, the Human Fertilisation and Embryology Authority (HFEA) sets no age limit on fertility treatment but doctors are obliged by law to consider the future welfare of any child, which in practice rules out mothers in their 60s. Since Bousada gave birth, two women in India who doctors said were aged 70 have had children following fertility treatment, both last year.

Prof William Ledger, head of the reproductive and developmental medicine unit at Sheffield University medical school and a member of the HFEA, said he believed cases like Bousada's might provide the impetus for closer controls.

"It's a shame that policy often comes from these individual tragedies. It's a very, very sad story," he said. "What's good about regulation in the UK is that we put the welfare of the child at the centre. There are many reasons to have misgivings about mothers so old, and I think this case has shown that we are right."

A 66-year-old new mother was "clearly pushing the boundaries of what nature intended", said Tony Rutherford, chairman of the British Fertility Society.

His own clinic, in Leeds, would not accept women for treatment who were over 45 as the chances of success with IVF were so small at that age, he said.

"Much beyond that, if someone gives birth you're effectively asking them to cope with a teenager, and all the problems that potentially comes with, when they're well into their 60s. This raises very serious questions."

Josephine Quintavalle from the Comment on Reproductive Ethics, a pro-life pressure group which campaigns on IVF issues in the UK, said the primary problem was a general unwillingness to accept the limits of ageing when it came to parenthood.

"We get older, it's the human condition, accept it. Move on to the next stage of life and live it to the full, but don't expect to be able to have children at any cost," she said. "If a woman in her late 60s announced she was going to go and play at Wimbledon she would be laughed at. Yet for some reason, when a woman of the same age decides she want to be a mother it's OK."

Bousada herself, who had never been married, told the News of the World that her family would look after the boys if she died. "They will never be alone," she said. "There are lots of young people in our family."