Ardern, 37, became prime minister last October after a whirlwind rise and then surprised the nation again in January by announcing she was set to become a mum for the first time.
Since then, the Pacific nation has been fascinated by the arrival of the baby while the PM has emerged as a role model for working mothers.
"The early stages were probably the most difficult because I had such bad morning sickness and at that point no one even knew," Ardern told AFP in Paris.
The Labour Party leader was visiting France during a week of meetings that will see her travel to Berlin and then London, where she will attend a Commonwealth Summit on Thursday and Friday.
"It hasn't changed my approach to my work. I'm a little slow going up stairs but I'd say that's about the end of it," she told AFP.
But a day of meetings about trade and security at the French presidential palace with leader Emmanuel Macron and a speech at Sciences Po university had also taken its toll.
"There will be a period when travel gets slightly more difficult, but I've been very focused on trying to minimise the impact because I have a responsibility to manage the government," she added.
Ardern's baby is due in June when she plans to take maternity leave for six weeks.
She will not be the first woman to give birth while leading a country.
Late Pakistani prime minister Benazir Bhutto had a child during her time in office in 1990.
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