National's Chris Luxon raised a few eyebrows over his comments about the nation's declining birth rate.

At an infrastructure conference, Luxon made a 'tongue-in-cheek' comment calling for more people to have babies to plug the worker shortage.

Massey University sociologist Paul Spoonley says Chris Luxon is right about the plummeting birth rate- but a middle-aged male encouraging people to have babies isn't a good hook.

"The reasons why we're not having babies is- we're seeing more women tertiary qualified, more women in the workforce, they're choosing to stick with their careers rather than having babies. It's a phenomenon we're seeing around the world."

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