Not surprisingly, the PM's office won't be giving any more formal announcements until Ardern and her partner Clarke Gayford get to officially announce the birth of their child, the sex of which they haven't let slip yet.
Just a handful of elected leaders worldwide have given birth while in office, notably Benazir Bhutto who had her son in 1990 while Prime Minister of Pakistan.
The pregnant Prime Minister arrived at Auckland City Hospital accompanied by her partner Clarke Gayford on Thursday morning.
The position of acting Prime Minister falls to current Deputy Prime Minister Winston Peters and will continue to remain that way while Ardern takes her planned 6-week maternity leave. Her expected due date was June 17.
The Prime Minister doesn't expect to be treated any differently to any other mum at the hospital.
The deputy leader of the National Party, Paula Bennett, wished Ms Ardern well in Parliament this morning.
Prime Minister Jacinda Ardern announced her pregnancy with a post on social media.
Ms Ardern assured she would still be on call, and the government would be business as usual. The couple have yet to reveal the baby's gender, but Ms Ardern was gifted the name Waru at Ratana celebrations and the name Waimirirangi was offered at Waitangi Day celebrations if the baby was a girl.