A mother whose baby son was born by prematurely by C-section after a horrific Nelson crash says she's grateful she got to spend five short days with him before life support was switched off.

The parents or the boy cannot be named due to a suppression order but say that the incident, which occurred on Nelson's Waimea Rd two weeks ago, has left them traumatised and suffering nightmares.

But while the mother says she feels robbed of her son, she harbours no hate towards the man charged in connection with the accident.

"As much as there is so much anger there is no hate. There is no point wasting that energy."

Up until falling pregnant, the couple was told it was unlikely they would ever have a child.

Two weeks ago, they were "in countdown mode" and ready to celebrate their new baby – she was 30-weeks pregnant. They were driving home from a friend's house when they saw headlights before the oncoming vehicle slammed into their car.

A head-on crash on Waimea Road, Nelson two weeks ago involved a couple counting down the weeks to the birth of their first child. (Photo / Supplied)

Her partner was driving and the shock sent the steering wheel into his chest, breaking his sternum.

"I just turned to her and asked, 'Are you all right babe'? She said 'no'."

Then he pulled off his seatbelt and kicked open the door of the crumpled car. He limped around to his partner's side and ripped open her door and knelt with her. Then someone tried to pull him away.

"That's when the pain shot through me and I just blacked out on the road."

His partner was rushed to Nelson Hospital where she was put under general anaesthetic and had her son via C-section.

"When he was born he was awake, eyes open and he was just so perfect," she said. "For the first five days we were living on hope and faith."

The morning after the accident the mother and her son were flown to Wellington Hospital. Over the course of the next few days, he deteriorated.

"We didn't know at first that he wasn't going to survive," she said.

Then, last Saturday the results of an MRI scan showed that there was severe bleeding on his brain and he wouldn't make it.

On that last day, they were finally able to hold their son.

"Up until his death he was still grabbing your fingers, he knew you were there," his father said.

"It was so heart-breaking to disconnect everything. It felt there was more we could do."

They said the support from all the hospital staff, Ronald McDonald House and the Flying Doctors, who transported them both from Nelson, had been incredible. They also wanted to thank their friends, family and the wider community for helping through what they say has been the worst time of their lives.

"It's the hardest thing we have ever had to deal with," the father said.

The mother said she still had nightmares about headlights and struggled to get back into a car.

But on Saturday they had a farewell for their son at the Gardens of Remembrance in Hope. They played music and let balloons go.

"It was a lovely send off," the mother said.

They were coping day by day and weren't sure how they would deal with impending court proceedings against the driver.

The baby's grandmother said she had taken heart at the response from around the country.

"That a nation is grieving with us. It's comforting to know you're not on your own."