Catherine will be about 25 weeks pregnant when the surgery is expected to be performed on December 29. However it is currently a waiting game for the couple.
Catherine underwent a number of tests at Mater Hospital yesterday, which will be sent to Vanderbilt Children's Hospital in America before the surgery is given the final go ahead.
"We are trying everything possible to make our son's life better. Even if we don't get accepted, we tried," Catherine said.
"Anyone who has a kid knows you would do anything for them."
The couple also hope to use their experience to pave the way for future parents whose children are diagnosed with spina bifida.
"If the surgery doesn't go ahead for us, it's about getting more awareness in the medical community in New Zealand," said Paul.
Catherine said doctors in New Zealand did not know the procedure was offered in Brisbane.
"It should be something that is offered here, not that you have to search around for," Catherine said.
The Harpers have experienced four miscarriages since their only child Jackson, 3, was born.
"It was devastating after what we've been through, that the only child who has stuck has severe issues."
Spina bifida is a birth defect in which the spine doesn't close properly during the first month of pregnancy.
"Baby Harper" has the myelomeningocele form of spina bifida, the most serious form of the disease, as well as a Chiari malformation, a structural defect in the cerebellum - the part of the brain that controls balance.
Doctors have told the Harpers the defect could mean their boy might not be able to walk, could have trouble controlling his bladder or bowel, have fluid accumulate in his brain and a tethered spinal cord.
But having the surgery could reduce the risk of death and brain damage, improve Baby Harper's chance of walking by 80 percent and reduce his need for some surgeries in the future.
"We were told if we don't do the surgery there is a 95 percent chance he will need a shunt, which is a tube from the brain to the tummy. If you have a shunt you are in and out of hospital all the time and will need a lot of surgery," said Catherine.
The surgery involves making a vertical incision in the mother's abdomen, to expose the unborn baby so doctors can perform the operation on its back.
The mother is then on bed rest until she is ready to deliver the baby, which must be done by C-section.
Spina Bifida Association of New Zealand executive director Diane Belcher said the procedure was a "game changer".
She researched it eight years ago when she was pregnant with her son, Daniel, who has spina bifida, and found it cost $85,000 in America.
As far as she could find, there wasn't any support for it in New Zealand at the time.
However, she now knew of New Zealand clinicians interested in the surgery and hoped its success across the Tasman would increase the chances of it becoming available here.
But surgery or not, parents had no reason to be fearful when they learned their baby would have spina bifida, Belcher said.
"Our children, young people and adults are living examples of people defying the expectations placed on them by doctors.
"Every day we have examples of achievements made that were never supposed to happen like walking, participating in sports, doing well in school, getting university degrees, getting married and having families."
The cost of the surgery is approximately $30,000 which Catherine said is "not really manageable".
"It's been a huge struggle but it's not really an option. We will find the money," said Paul.
The Harpers have applied for funding through the New Zealand and Australian governments, but have had to go ahead with the surgery privately in order to get it in time.
• To support the Harpers, go to https://givealittle.co.nz/cause/babyharper#
