Canberra family welcomes newborn weighing more than 6.2kg

But sure enough Aubrey Seamus Brady, born March 3, was that big.

He weighed almost double the average weight of an Australian newborn, which is 3.3kg, or 7.2lbs, and is about the size of an average three-month-old baby boy.

Unsurprisingly, Aubrey was delivered by a planned caesarean section.

Aubrey's father, Jim Brady said in the delivery room the staff were clearly stunned.

"The obstetrician could barely pick him up," he said.

"The midwife in the background just opened her mouth."

Aubrey was not born late, in fact he did not even make full term, he was born at 38 weeks.

"I dread to think what would have happened if I had gone to full term," Ms Brady said.

"I felt uncomfortable, particularly towards the end of the pregnancy but I didn't have any inkling he would be as big as he was."

Ms Brady expected to have a big baby. Aubrey was the third child for the couple and both of the older sons were born at an above average weight.

"I have type one diabetes so we always knew they were going to be on the heftier side," Ms Brady said.

"I was extremely well controlled this pregnancy compared to other pregnancies but doctors said it's just part of the course ... you are going to have heftier babies and apparently they do get bigger with every pregnancies."

The Brady's first born, Henry, 5, weighed 4.4kg when he was born prematurely at 35 weeks and Leo, 3, weighed 5kg.

Despite their hefty birth weights, Ms Brady said both Henry and Leo were lean today.

"They are both little string beans full of energy," she said.

With three boys, the Bradys are halfway to their own Brady Bunch but Ms Brady said they would not look to complete the bunch.

"I think this is it, this is the sign from nature to say you know what you have maxed out," she said.

Friends and family of the Bradys have been taken aback by the size of Aubrey.

"They have a lot of questions like 'did you deliver naturally'," Ms Brady said.

At 6.225kg, Aubrey is likely one of the biggest babies to ever be born in Canberra.

However, he is still a bit off the biggest baby to be born in Australia - a baby clocked in at 7.399kg in 1963.

Aubrey was in the Neonatal Intensive Care Unit at the Centenary Hospital for Women and Children until Sunday night. He had some trouble with his lungs and his blood sugar also needed to be monitored.

Centenary Hospital registered nurse Rowena Espiritu said being in the NICU she was used to small, premature babies so it was a different experience to look after a baby so large.

Aubrey even needed his own cot brought in as the ones in the NICU had a weight limit of 5kg.