An Albion Park couple has shattered the medical odds after giving birth to naturally conceived identical triplets - a combination thought to occur only once every 160,000 births.

Xavier, Cooper and Noah Billing made their entrance at Sydney's Royal Hospital for Women from 11.42am yesterday, weighing 1.7kg, 1.56kg and 1.5kg respectively.

Their arrival came at 32 weeks and two days gestation, and to the delight of parents Lisa and Keiran Billing.

"They're so delicate," said Mr Billing between visits to the boys' humidicribs yesterday.

"You can hold them in the palms of your hands they're that small," Mr Billing said.

Triplet births are rare, accounting for 0.3 per cent of Australian pregnancies according to the most recent published data, from 2007.

But identical triplets are far less common, as are those conceived without the use of fertility drugs.

The question of how rare has inspired a wide variety of estimates, with figures anywhere up to 1:200 million doing the rounds on the world wide web.

However Wollongong obstetrician and fertility expert David Greening favours the British Multiple Births Association statistics odds of 1:150,000-160,000.

"Being identical makes this particularly rare," he said.

"I've only seen one (naturally conceived identical triplet birth) in 15 years.

"It's one of the amazing things that nature throws up sometimes.

"It's going to be an amazing experience bringing them up. All the very best to them."

Incredibly, it took three visits to two different obstetricians for the Billings to learn the full extent of the pregnancy.

Their first doctor indicated a single birth, then at their next appointment told them to expect twins.

Mr Billing, 29, learnt there was a third baby after returning home from work to a sobbing wife fresh from her third visit.

"Thank God they stopped there," he said.

The couple have bought a bigger car and extended their house in preparation for the triplets' homecoming in several weeks' time.