"By that time she had stopped twitching and the doctor who examined her could find nothing amiss and thought she probably had a bit of a cold. I thought I'd overreacted. It was only as we turned to leave that she began twitching again and the doctor immediately called the children's ward for help. By this time you could see that Ava Rose's skull was starting to swell, and I was getting quite panicky."
Using drugs administered through an infusion pump, doctors put the baby into an induced coma in order to protect her brain from possible damage caused by the unexplained swelling, while they ran a battery of tests to find the problem.
"At first they thought it was meningitis, but a lumbar puncture came back clear. An ultrasound of the soft spot on her head to look for fluid on the brain was also negative," says Purdy.
Finally, doctors did an MRI scan, which revealed a blockage in one of the blood vessels in Ava Rose's brain. She had suffered a stroke.
"I'd never heard of a baby having a stroke and couldn't take it in at first," says Purdy, 32, who lives in the town of Retford.
"Other members of the family had had strokes, but they'd all been over 60 and, like most people, I just associated the condition with old people."
Yet according to the Stroke Association, five out of every 100,000 children up to the age of 18 in Britain will have a stroke each year, including an estimated one in 4,000 newborns. Strokes can even occur in the womb, in the last eight weeks of pregnancy.
Locally, about 40 strokes a year are suffered by children in New Zealand. Nearly 2000 (a quarter of all strokes) will be suffered by people under retirement age, according to the New Zealand Stroke Association.
"It's one of the major causes of disability in children and has one of the top 10 mortality rates among children," explains Dr Finbar O'Callaghan, consultant paediatric neurologist at Great Ormond Street Hospital for Children in London. "Childhood stroke is most common in the first year of life, then it drops off, and rises again in the teens."
In babies up to 28 days old, these are called perinatal ischaemic strokes. They are usually caused by clots breaking off from the placenta and lodging in the child's brain, as doctors believe happened in Ava Rose's case. (She was later found to have a hole in the heart - called an atrial septal defect - but it is uncertain if this was associated with her stroke.) In older children, strokes are often linked to an existing condition like congenital heart disease.
Among the adult population, stroke symptoms are easy to detect, but diagnosing a stroke in babies is far more difficult. The campaign Fast was launched in 2009 by Public Health England and the Stroke Association to help people identify signs of a stroke. The acronym stands for Facial weakness, Arm weakness, Speech difficulty, Time to call 999. Unfortunately, this checklist is hard to apply to barely mobile infants.
"Strokes in the first few weeks of life are often missed and only picked up when a child doesn't seem to be developing as expected or is displaying a weakness down one side," explains Dr O'Callaghan.
"Unlike in your granddad, where it is immediately obvious if he is unable to move his arm, symptoms are much harder to detect in newborn babies, who are sleeping most of the time."
The common delays in detecting a stroke also mean babies like Ava Rose are rarely given the anti-clotting drugs that are used in adults, when a stroke is discovered within four to six hours.
Two months after her stroke diagnosis, Ava Rose was also diagnosed with epilepsy, a condition commonly associated with stroke in babies, triggered by scarring of the brain tissue. She was found to be suffering with mild cerebral palsy, too - another result of brain damage caused by the stroke.
"Over the next few months we were constantly calling out ambulances, and barely a week went by that we weren't in hospital," says Purdy.
"She kept having episodes where her jaw and upper body would stiffen for a few moments and then she would howl. I didn't recognise it at the time, but now know these were seizures."
Ava Rose is on anti-epileptic drugs and can be given a sedative as a "rescue remedy" when she does fit. But because she is growing, getting the dosage right is tricky.
"Doctors can prescribe one dosage, then in four weeks she has grown and needs a different prescription," says her mother.
Ava Rose is now three and needs round-the-clock care: Purdy has given up her job as a cleaner and husband Daniel also stopped working as a landscape gardener.
"Ava Rose can't be left alone at any time in case she has a seizure," says her mother.
"She sleeps in a bed pulled up against my bed and I can't really rest as I need to stay alert."
Often, through the night, Ava Rose has myoclonic seizures - brief shock-like jerks that cause her to cry out in pain.
"And because of the cerebral palsy she can't turn herself over, so I have to turn her every time she moans. If I'm up all night, Daniel will take the other children to school, then come back and try to get Ava to sleep on the sofa while I do housework. It's hard at the moment and there are lots of things we can't do as a family because Ava's stroke means she can't walk as well as a typical three-year-old, and her speech has been delayed."
There is light at the end of the tunnel, though. Ava Rose goes to a local nursery, where she has a specially assigned one-on-one carer, and Purdy hopes she will be able to attend mainstream school. She is also having physiotherapy to help strengthen her muscles, and speech therapy.
"She crawled at eight months and is developing into a caring and inquisitive member of the family," says Purdy.
She takes encouragement from the words of her consultant, Dr Chris Rittey at Sheffield Children's NHS Foundation Trust. He says that the management of Ava Rose's seizures has significantly improved recently and "her development is coming along very well".
There is still a long way to go in recognising childhood strokes, and supporting the families who endure them. The Stroke Association has set up a three-year initiative called the Childhood Stroke Project to identify and help meet the needs of families affected.
Happily, according to Dr O'Callaghan, the plasticity of babies' developing brains makes them better able than adults to recover from a stroke.
"Half of all babies who suffer a stroke in the first year of life will make an excellent recovery and you will never even notice that they have had a stroke. And more than 90 per cent will also walk in the first year."
He urges parents to trust their instincts. "Parents should get any type of movement in a baby that appears unusual checked. Babies can have jittery movements and for first-time mothers especially, it can be difficult to know how a baby is supposed to move. But anything that seems unusual should be investigated as quickly as possible."
For more information about stroke visit www.stroke.org.nz
