At eight days, she was taken to the Royal Brompton Hospital in London after doctors feared she had a hole in her heart. Cassy and her husband Graham, from Tilbury, Essex, could do nothing but pray.
"I didn't understand what was going on," says Cassy now. "We didn't feel able to ask, because we didn't want to distract their attention. All I knew was that my daughter was very sick. We thought she was going to die."
At the Brompton, the couple were informed that Claire had been born with a rare condition, "tetralogy of Fallot", in which the child has four major defects, and that she would need an operation to let blood through to her lungs. The operation was a success and at five weeks Claire was allowed home. Her problems, though, had just begun.
Two weeks later, something set off the Stantons' burglar alarm, and Claire, who was lying right underneath it, showed no reaction. "It felt like the end of the world," remembers Cassy, who realised at that moment that her baby was also deaf.
Worse was to come. One month later doctors discovered that Claire was only partially sighted. "We were beginning to think, 'What next?' No one could have this much bad luck. That was when I first thought there had to be a reason."
Three months later, at the Hospital for Sick Children at Great Ormond Street, Cassy's suspicions were confirmed when the genetics consultant, Dr Baraitser, diagnosed Charge syndrome, an acronym for six major abnormalities. The syndrome affects a relatively small number of children, who suffer from heart disease and a blockage of the nasal passage due to bone material or a membrane. Additionally, their growth is retarded. Research into the condition has been limited, because it is so rare. "Once we had a label, we knew we were getting somewhere, rather than stumbling around in the dark," says Cassy.
Her consultant, having ruled out any hereditary explanation, then asked her about her job. Many parents of Charge sufferers, he said, were convinced that there was a link between the syndrome and exposure to certain pesticides. In particular, they believed that an organophosphate pesticide might be the cause, but there was no evidence as yet to support this.
At the time, Cassy dismissed the possibility, but after chatting with the mother of a Charge child who worked in a school that had been sprayed with insecticide, she began to make her own connections. Hadn't her office been sprayed by a pest control contractor following an infestation of cockroaches?
In dread of what she would discover, she ploughed through company papers and found that her office had been sprayed on the 38th day of her pregnancy. She learned, also, from medical literature, that the developing foetus is at risk from Charge syndrome between days 35 and 45. "To pinpoint the visit from the pest control guy right in the middle of the danger period was terrifying," she says.
When she asked what chemicals had been used, Cassy was told that an insecticide containing permethrin had been sprayed. Cassy was unable to obtain a copy of the contractor's invoice, either from her employer or from the contractor.
Bent upon discovering whether the chemical had caused Claire's condition, and if so determined to see it banned, she applied for and was granted legal aid for Claire, and instructed a solicitor to investigate any possible causal link.
Cassy, for her part, wrote to the Advisory Committee on Pesticides explaining her concerns. She was informed that the Department of Health looked into such cases, so her letter had been forwarded. A response from the Department of Health reassured her that it was unlikely she had been affected by the insecticide, but there were cases of individuals who were especially sensitive to certain chemicals, so they would be sending her letter to the Health and Safety Executive. Three weeks later, Cassy received correspondence from the HSE, who, she was told, would be sending her letter on to the Advisory Committee on Pesticides. Her letter had come full circle.
Cassy learned that a medical survey of Charge children conducted in 1993 showed that 36 per cent of mothers "reported contacts with pesticides and insecticides in the early months of pregnancy".
In 1994 and 1995, Britain's Health and Safety Executive investigated complaints of ill health as a result of exposure to permethrin , normally used as a timber treatment or an agricultural pesticide. People complained of feelings of nausea skin irritations, and breathing difficulties.
The medical experts consulted by Cassy's solicitor had been unable to find conclusive proof of a link, but they strongly believed that there was a need for further research. .
Little Claire, meanwhile, in spite of delayed physical development, was showing great cognitive improvement. At 20 months she had learned sign language and started to talk. At three she was able to count to 100 and recite the alphabet in spoken, written and sign form. Her progress stunned professionals. She was sent to a playgroup and then on to mainstream nursery school, where she showed signs of a high IQ.
During this time, Cassy's solicitor had been unable to get hold of the contractor's invoice and he told her that, in his opinion, the case would be difficult to prove. Cassy found this hard to accept.
More disturbing yet was evidence that the contractor - a one-man-band who earned a living, when he was not spraying offices, by doing furniture removals - had no insurance cover so there would be very limited prospects for recovering any damages.
In early 1995, Cassy joined the environmental pressure group the Green Network, who lobbied Parliament on the issue, but the Government responded that there was no link.
Cassy contacted her local Labour MP, Andrew Mackinlay. "I was amazed when Cassy first told me her story," he says. He decided that it warranted his own investigation and an airing in the House of Commons.
In response, Tom Sackville, then Parliamentary Under-Secretary of State for Health, blamed the "irresponsible media" for whipping up a scare regarding pesticides, and trumpeted, "We have the best regulatory system in the world."
It was the kind of reply Cassy Stanton had come to expect. She was not prepared, however, for what would happen next. The contractor now claimed that he had not been spraying permethrin to kill cockroaches, but another preparation, which is simply ionised soapy water, and is normally used to reduce the build-up of static electricity on carpets.
More astonishing yet was the arrival through the post of a copy of the contractor's invoice - three years after Cassy first requested it. It raised more questions than it answered. There was no reference to the chemicals used to - in the words of the contractor - "de-infest fleas".
"All the evidence he had given contradicted itself," says Cassy.
The minor triumph of having obtained a copy of the invoice was soon overshadowed by concerns for Claire, who, in January this year, at the age of almost four, went back into the Royal Brompton Hospital for a long- awaited operation to rectify her heart problem. She had made such strides in her short life, doctors were fairly confident that she would come through the ordeal. Although the operation was a success, Claire developed complications. Her lungs had been clogged with blood, she had to be put on to a ventilator. Seven days later, she died.
"We always knew there was a risk of losing her," says Cassy, "but I was devastated. She was a lively, intelligent, loving, active little girl. Everything I had, just went in an instant."
Cassy's hopes of learning the truth died with Claire. Her legal aid was withdrawn. "I can't afford to sue. And unless a medical expert proves these things are safe, or not safe, children may go on suffering.
"Claire suffered. Her life wasn't easy. But I'm damn sure it won't have been in vain. What price are we putting on our children's safety?"
Mr Mackinlay still has worries about the safety of some chemicals used in pesticides. "I am particularly concerned about new - and relatively new - pesticides. I am worried about the testing procedures. I want more research done and will be pressing hard for it."
Mr Mackinlay would like to see the burden of proof shifted on to manufacturers. As he says, why should it be left to the Cassy Stantons of this world?