Jacinda Ardern is making history again, with ease.

As if going from Labour leader to Prime Minister in less than three months wasn't enough, she is going to give birth in June, the first for a New Zealand Prime Minister.

From her statement, it was clearly unplanned.

The timing is interesting. The 37-year-old found out she was pregnant a week during the intensity of coalition negotiations, and a full week before New Zealand First Winston Peters announced she would be Prime Minister.

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There may be people – Mark Richardson perhaps – who believe Ardern should have declared her pregnancy before she took up the PM's post. But there is no strong argument for it.

She certainly made it clear before the election that she had hopes of being a mother – and there was no suggestion that she was going to postpone simply because she had taken a leadership role in Labour.

She told Peters about the pregnancy only yesterday and he will step into her place as Acting Prime Minister for six weeks.

The prospect of Peters being in charge for six weeks is hardly cause for concern. If anything, the concern should be that she is taking too brief a break for the fog to lift after giving birth.

Unplanned as it was, the timing is very good for Ardern. She will leave after the Budget in May and in between major travel commitments to London in April for the Commonwealth Heads of Government Meeting and Apec in November

Also importantly, assuming she has no more babies this term, she will go into the 2020 election with a toddler in tow rather than a needy new baby.

By that stage, she may well be looking like superwoman.