Shannon Manunui; when she dropped well below her birth weight of 420 grams, she was not much bigger than a can of Coke.

Baby Shannon dropped well below her birth weight of 420g. Photo: Supplied

When tiny Shannon Manunui and twin brother Liam came into the world last year at just 26 weeks gestation, they smashed the records at Canberra Hospital. Born via emergency caesarean, Shannon was the smallest surviving baby ever born at the hospital, weighing just 420g and small enough to fit into the palm of an adult hand.

Grave fears were held for the health of the twins, but looking at them rolling around happily on their family's living room floor shows what an amazing difference a year can make. 

The Manunui twins have just passed a major milestone by celebrating their first birthday, and so far both are in good health.

Liam (in the red) and Shannon Manunui - the twins are healthy, having just celebrated their first birthday after premature birth last year.?

Twins Liam (in the red) and Shannon Manunui. Photo: Supplied by family.

Shannon, now a hearty 5.5kg, dropped to a low of just 386g after her birth. Liam, born at 620g, is now 6.8kg, and is doing so well that there are few signs left showing he was a very premature baby.

There are no discernible differences between Liam and a one-year-old born after a normal nine-month gestation.

"In fact, Liam is slightly ahead even on his uncorrected age," said mum Leanne. "Everybody is very happy with the progress of both of them, no long-lasting problems have been identified."

More than 500 sick babies have been admitted to Canberra Hospital's new neonatal intensive care unit since it opened almost a year ago.

The smallest babies can spend as long as 100 days in the unit, according to nurse Kelly Munstermann, who advises parents of pre-term babies to be patient as they watch their newborns develop.

"Every pregnant woman wants a healthy, fat, chubby baby but [in this unit] it's two steps forward, one step back," she said.