Prime Minister of New Zealand Jacinda Ardern is expecting her first child in June.
Ms Ardern says partner Clarke Gayford will stay home as the primary caregiver.
"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.
"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."
Ms Ardern said she and Mr Gayford are particularly lucky - they had been told they would need "help" to become parents.
"We first knew of my pregnancy on October 13, but as many couples do in the early stages, we kept it to ourselves," she said.
Ms Ardern became Prime Minister of New Zealand on October 19. She has been pregnant the entire time she's been in office.
"From a personal perspective, I am so looking forward to my new role as a parent, but I am equally focused on my job and responsibilities as Prime Minister.
"While 2018 will be the year I become a mum, it will also be a year that the Government finishes our 100-day plan and starts pursuing all of the priorities that will build a better New Zealand.
"I look forward to leading that work and having a slightly expanded family join me on that journey."
Sharing the news on Instagram, Ms Ardern said: "Our team will expand from two to three.
"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."
Ms Ardern is not the first Prime Minister to expect a child while in office. Pakistan's Benazir Bhutto had a baby in 1990, while Prime Minister.