Stuart's son Nix was born prematurely at just 31 weeks, "ironically", as his mother Amber said, on World Prematurity Day, which is observed on November 17 each year.

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Stuart left his property in Laggan at 4am and planned to run the 55km through Crookwell into Goulburn and home again.

Not considering himself much of a runner, Stuart said the longest run he'd ever completed was 21km.

"I've been training for a month," he said.

However, training for an ultramarathon in just four weeks is not a lot of time.

"It's harder than I thought but I'll get there ... my feet and knees are hurting," Stuart shared on social media.

Stuart was already a few kilometres out of town when the Post caught him for a photo on his way back to Laggan at about 1.30pm.

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During Stuart and Amber's time in the hospital with their son Nix, they came across a pamphlet for Running for Premature Babies and have joined running fundraisers nearly every year since.

Running for Premature Babies was founded by Sophie Smith and her late husband Ash after they lost their prematurely born triplets to complications after their birth in 2006.

In Australia, one in 10 babies are born prematurely, which equates to 26,000 babies every year. Many of these babies require Neonatal Intensive Care, which can cost anywhere between $3500 and $10,000 per baby each day.

"We learnt that most machines in neonatal intensive care units are donated and hospitals rely significantly on fundraising," Amber said.

To express their gratitude for the donated equipment that helped save their son, Stuart and Amber have raised around $20,000 over the past five years.

Stuart's 105km run this year has attracted just under $12,400 in donations so far.

To donate to Team Nix you can go to: https://www.runningforprematurebabies.com/fundraisers/teamnix/premmie-marathon-challenge.

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