She says becoming a parent hasn't changed her views on specific government policies, other than reinforcing her view that there needs to be a clear and strong focus on supporting families.

"We believe ourselves to be clean and green. We believe ourselves to be fair-minded, to have a strong sense of social justice, and we think we're innovative," she said.

"Actually, we need to do a lot more to make that a reality."

Ms Ardern flew back to the nation's capital, Wellington, from her home in Auckland on Saturday.

She told reporters she and her partner Clarke Gayford would be spending the next few days preparing Premier House - New Zealand's official prime-ministerial residence - for a baby.

"I guess (it's) the first time it's probably had a little one there. We'll be pulling together all of the second-hand furniture our friends have passed onto us for Neve," she said.

"It is an old home, but it is a very warm home."

Ardern, 38, is just the second elected world leader in recent history to give birth while holding office.

The last leader to give birth while holding office was the late Pakistan Prime Minister Benazir Bhutto, who gave birth to Bakhtawar in 1990.

Ardern said she will feel rested enough when she returns to the capital.

"I'm getting sleep mostly because I'm sharing the load with others, and I'm very grateful for that," she said.

"By that I mean Clarke. We're doing the job together."

Australian Associated Press