"He's not bad considering how early he is...He needed to come early because he wasn't doing too well'' said mum Sian, a GP.
Oliver's dad, Joe, who works as a neurologist at Waikato Hospital said the birth of his son - the couple's first child - had been a surreal experience for them both.
"Everything happened a lot earlier than we thought and we were thrown in the deep end a bit,'' he said.
"But when things settled down it was amazing.''
The couple, who moved to New Zealand from Wales about three years ago, hoped their little boy would grow up to be a "proper little Kiwi kid'' who is happy and healthy.
They have already shared the news with family back in the UK, who had just seen in the new year themselves, via Skype and Viber.
Asked how they would celebrate, Mr Merola said "is sleep a way of celebrating ?''.