— -- In a rare occurrence, an Australian mom has given birth to a second set of identical twins.
"When my doctor found the second heartbeat, I just couldn't believe it," Simone Burstow of Brisbane told ABC News by email. "I was laughing and crying at the same time and I just kept asking him, 'How does this happen?'"
Evie and Georgia were born on Sept. 4 to Simone and John Burstow.
The girls join their 4-year-old big brothers, Harrison and Oliver, also identical twins, who were born May 15, 2012.
"My obstetrician is Dr. Rob Butler and yes, he was shocked to discover I was having my second set of identical twins," Burstow said. "He had to triple check when he did the scan to make sure he was seeing it correctly."
Burstow said that her sons Harrison and Oliver are good friends and that Evie and Georgia are content, relaxed little babies.
"As they get older, we see more and more of their different personalities," she added.
And while she has her hands full with four kids, Burstow said she wouldn't have it any other way.
"Being a mum makes you take a step back and focus on what is really important and not to get too caught up in the small stuff," she said. "I love the conversations and adventures I get to have with my 4-year-olds and I just love enjoying the time I have with my little girls and trying to enjoy every stage -- even the night wake-ups and lack of sleep. I know these stages don't last long and as I don't think we will have any more children. I'm trying to savour every moment!"