National leader Simon Bridges isn't apologising for saying the Prime Minister's newborn daughter will be made to go to school in boys' clothes.

Jacinda Ardern and partner Clarke Gayford welcomed their first child into the world on Thursday. During an interview with rock station Radio Hauraki the next morning, Mr Bridges joked that by being born in a public hospital, had cost the country "a lot" of money.

He then said he'd try and turn young Neve Te Aroha Ardern Gayford into a National supporter.

"Just because there's pinko ideas in the parents it doesn't mean the baby's taking those on board," Mr Bridges said, suggesting Ms Ardern had "funny ideas" after spending "too much time in universities".

Newshub political editor Tova O'Brien said in an opinion piece the Oxford-educated ex-lawyer with two degrees should "unreservedly apologise" for the comments, calling his views "loutish, transphobic rubbish".

Asked on The AM Show if he'd apologise, Mr Bridges said he wouldn't be.

"It was incredibly light-hearted and intended that way - an interview on Radio Hauraki. But I wish Jacinda, her partner and little Neve all the very best. Just absolute happiness.

"Look, I know as a father of three little ones what a special time [they're having]. I've got a six-month-old - beautiful, precious little Jemima - so I know just what a special time this will be for them."

He said anyone who watched or listened to the whole interview would "see the context and understand what it is".