She said her husband is to be a "stay at home" dad.
"We thought 2017 was a big year!"
She says she first learned of the pregnancy six days before she was elected in October, and she's expecting her child in June. She added she meant to be "fully contactable" during her maternity leave and that she meant to resume "all prime ministerial duties" once her leave ends.
New Zealand has long held a progressive reputation, having been the first country to give women the right to vote in 1893."It's awesome timing...125 years later we have a prime minister who's going to give birth in office", said Minister for Women Julie Anne Genter.
Her answers seemed to resonate with many people, some of whom pointed out that under New Zealand law, workplace discrimination on the basis of pregnancy is illegal.
Shipley added: "It will bring special insight I suspect in her work and joy to her family".
The Prime Minister also signalled that she was planning to donate some of her maternity leave money to Plunket.
"Aside from her infectious excitement, it's refreshing to see her so deftly sweep aside any potential arguments that she can't be both prime minister and a mother".
Two of New Zealand's former prime ministers were among the first to offer congratulations.
Australian Prime Minister Malcolm Turnbull sent "lots of love and best wishes from me and Lucy and all of us across the ditch".
After the six weeks, she will resume all her prime ministerial duties.
During a press conference with Gayford by her side, Ardern also gave some perspective on the fact that she'll be the first world leader to give birth in office in almost 30 years. "I am about to sympathize with them as I sympathize with all women who suffered morning sickness".
"Acknowledgement that actually, it's our family members who often don't get to interact with everyone else and so it's a really nice opportunity to bring everyone together - so, this isn't a first".
In 1990, Benazir Bhutto gave birth to a daughter while serving as Pakistan's prime minister.