Instead, she gave birth to baby Sienna beside the F3.

Health authorities are investigating why Mrs Egan was sent home from Wyong Hospital last week when she was in pain and experiencing regular contractions.

Mrs Egan, of Chain Valley Bay, contacted Wyong Hospital at 8pm last Tuesday to advise she had been in labour all day and was having five-minute contractions.

"They sounded disinterested and said 'well I guess you can come in for an assessment'," she said.

She was examined at the hospital later in the evening after her contractions became stronger.

"She [the midwife] advised me to go home," Mrs Egan said.

Despite writhing in pain, Mrs Egan said she felt scared to return to the hospital again.

At 2am on Wednesday her husband helped her into their car and began a desperate dash to Gosford Hospital.

"It got so unbearable laying on my back that I had to sit up on my hands and knees," she said.

Her waters broke near the Ourimbah exit and she gave birth to a healthy girl, Sienna, before an ambulance arrived.

Mrs Egan has made a formal complaint to the health service.

"The woman who sent me home at Wyong talked to me like she had just come out of uni and was reading from her text book," she said.

"It is important that these midwives understand that each individual is different and that they can't make first-time mums feel like they are a nuisance."

A Northern Sydney-Central Coast Area Health Service spokeswoman said the health service has begun an investigation into Mrs Egan's experience.

"The health service apologises for any distress experienced by Mrs Egan and her husband during the recent birth of their daughter," she said.