"We weren't sure it would happen for us." NZ PM Jacinda Ardern announces pregnancy.

New Zealand Prime Minister Jacinda Ardern has announced she is expecting her first child.

In a post on Facebook, 37-year-old Ardern says she will be joining the many parents out there “who wear two hats”.

“And we thought 2017 was a big year! Clarke and I are really excited that in June our team will expand from two to three, and that we’ll be joining the many parents out there who wear two hats.

“I’ll be Prime Minister AND a mum, and Clarke will be ‘first man of fishing’ and stay at home dad. I think it’s fair to say that this will be a wee one that a village will raise, but we couldn’t be more excited. I know there will be lots of questions, and we’ll answer all of them (I can assure you we have a plan all ready to go!) But for now, bring on 2018.”

In an official statement, Ardern outlined her plans to take six weeks of maternity leave when the baby arrives in June.

“We’re both really happy. We wanted a family but weren’t sure it would happen for us, which has made this news unexpected but exciting,” she said in a statement, according to Stuff.co.nz

“Yesterday I met with Deputy Prime Minister, Winston Peters, to share the news and to ask him to take on the role of Acting Prime Minister for a period of six weeks after our baby is born.

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“As is the case when I am overseas, Mr Peters will act as Prime Minister, working with my office while staying in touch with me. I fully intend to be contactable and available throughout the six week period when needed.

“Mr Peters and I have a great relationship, and I know that together we’ll make this period work. I will make arrangements for appropriate Ministers to act in my other portfolios over the six weeks I am away from Parliament.

“At the end of my leave I will resume all Prime Ministerial duties,” she said.

She went on to express her gratitude that her partner Clarke, a television presenter, would be able to stay home with their baby.

"Clarke and I are privileged to be in the position where Clarke can stay home to be our primary caregiver. Knowing that so many parents juggle the care of their new babies, we consider ourselves to be very lucky.

"We consider ourselves lucky for another reason. Clarke and I have always been clear we wanted to be parents but had been told we would need help for that to happen. That's made this news a fantastic surprise.

"We first knew of my pregnancy on the 13th of October, but as many couples do in the early stages, we kept it to ourselves."

In October last year, Ardern was officially sworn in as Prime Minister.