Prime Minister Jacinda Ardern is likely to miss out on her government's planned extension to paid parental leave.

Ardern posted on her Instagram account today that her and partner Clarke Gayford were expecting a baby in June.

"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.

READ MORE: Jacinda Ardern announces she's pregnant

"I'll be Prime Minister AND a mum, and Clarke will be 'first man of fishing' and stay at home dad," she posted.

But the timing of the baby's arrival means Ardern or Gayford will likely miss out on the increase from 18 weeks to 22 weeks - which doesn't kick in until July 1.

The extended scheme will then stretch further to 26 weeks from July 2020.

Ardern is not the first leader of a state to be pregnant while in office.

Former Pakistani Prime Minister Benazir Bhutto had her second child in 1990 - becoming the first modern head of government to give birth while in office.

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.

A post shared by Jacinda Ardern (@jacindaardern) on Jan 18, 2018 at 1:44pm PST