Two and a half hours later, she was cradling the baby health experts told her she could never have.

Mrs Walsh gave birth to daughter Shelby at Fairfield Hospital, in Sydney's west, after her GP stunned her with the news that she was not only pregnant but also about to go into labour.

Mrs Walsh, 38, suffers from polycystic ovary syndrome, a condition that causes testosterone imbalance, triggering a range of symptoms such as obesity, irregular or no periods, acne, excess hair growth – and infertility.

During her 15-year marriage to husband Anthony, she was told many times that she would never conceive naturally.

"My husband was parked outside the surgery. I climbed into the car. He asked: "How did you go?" I told him: "You're going to be a father ... today."

In a state of "sheer disbelief", the couple headed straight for the hospital at 2pm. At 4.30pm, they were parents.

While the hospital's head of obstetrics and gynaecology Charles McCusker doesn't like to use the word "miracle" freely, he said Shelby was exactly that because of the "unusual" and "inspirational" chain of events that resulted in her survival.

"What an incredible gift for two of the most wonderful, genuine, people you could ever wish to meet," Dr McCusker said. "Even to a gnarled old timer like me, she is a cute baby."

He spoke of the countless "crossroads" on August 11 which, even before the family's arrival at the hospital, could so easily have resulted in "disaster". Had Mrs Walsh attempted to see out her pain at home, or had her GP stuck with his original diagnosis and not conducted a precautionary pregnancy test, "the outcome would have been tragic," he said.

As shocked family members arrived at the hospital, they were confronted with news of a "dire emergency".

Mrs Walsh's mother, Gale, said: "The doctor informed us they had to get Kim upstairs straightaway. We had two minutes to see her. There was a lot of panic ... and a lot of questions."

Dr McCusker said when Mrs Walsh arrived at the hospital, she weighed 170 kilograms and her baby was in "acute foetal distress".

As the picture became clearer, it emerged that the umbilical cord had become wrapped around the foetal neck.

"Aside from myself and my junior staff, the entire midwifery team were on board," Dr McCusker said "I brought in a trusted senior colleague, Dr Harry Ngo. Anaesthetic staff were able to provide a reasonable anaesthesia, despite obvious difficulties. And then of course there were the paediatrics staff. It really was a case of Team Fairfield pulling together. Shelby arrived into this world surrounded by relief, joy and incredible happiness."

In the days that followed, the couple were "overwhelmed" by the generosity shown by friends as well as strangers. "We walked in the door without so much as a nappy. But everything we needed – and more – has since arrived through the goodwill of others," Mrs Walsh said.

A fortnight ago, the two proud parents returned to Fairfield Hospital with their beautiful daughter to say "a big thank you" to staff. Mrs Walsh later posted a Facebook picture of Dr McCusker holding Shelby, introducing him as "the man who saved mine and my daughter's lives".

twitter: @eamonnduff