And why not? Not only did Ardern and her partner, TV presenter Clarke Gayford, seem so happy to be expecting their first child, but Ardern is blazing a trail here. She's only the second world leader, after Benazir Bhutto, to have a baby in office.

But while much of the focus has understandably been around Ardern's "girl power" moment, she is not the only role model here. Gayford will be the primary carer of their baby after six weeks. So there is also a huge opportunity to show people that fathers can also be the one to stay at home.

Victorian Labor MP Clare O'Neil got her first frontbench role in 2016, when she was eight months pregnant with her second child. She returned to work eight weeks after giving birth, with her partner, Brendan, a former doctor and now student, taking the lead role in looking after baby Louis.

"To me, what Clarke and Jacinda are publicly doing is massive. Dads taking the primary care role needs to be seen as normal," O'Neil says.

"If we we want to see gender equity, we need to see more blokes stepping up and taking charge of households."

The Australian Institute of Family Studies says "stay at home fathering is not a common approach in Australia", with the term describing only about 4 per cent of two-parent, opposite-sex families (with children under 15), as of mid-2016.

While parental leave entitlements for fathers are improving (albeit off a very low base), recent reports suggest men are not embracing the leave they have. The government offers new fathers two weeks' pay at the minimum wage, but since this was introduced in 2013, there have been concerns about low uptake. According to the Australian Bureau of Statistics, 95 per cent of primary parental leave in the private sector (which is taken by the person who has the most day-to-day responsibility for a child) is taken by mothers.

Any woman who has had a baby will not be surprised by these figures. A new mum is asked what she will do about work (how much time will you take off/ will you even come back/ how will you manage a baby and your job?) from the time she declares she is pregnant. Dads might be politely asked if they plan to take a a couple of weeks off to help with nappies when the baby arrives. But it is never assumed their careers will suffer any major interruptions.

Research suggests we are still clinging tight to ideas about men needing to earn the money. And that looking after the babies is still seen as a woman's job.

A 2016 Monash University study surveyed 951 fathers who were the main income earners in their households. Only 16 per cent of respondents felt dads were "as accepted" as carers in workplaces as mums. Almost 90 per cent said they felt pressure to earn the family's money, even though only 33 per cent thought it was "natural" they be the primary breadwinner. It also found that 85 per cent were open to taking three or more months leave to look after their baby, but only if there were no financial barriers.

Meanwhile, a 2014 Australian Human Rights Commission survey found 27 per cent of fathers reported workplace discrimination around things like taking parental leave and flexible work arrangements (the rate was about 50 per cent for women).

Former Greens senator Larissa Waters made history last year when she became the first Australian politician to breastfeed in Federal Parliament. While she was rightly hailed for her efforts, she was also supported by her partner, Jeremy, who had taken leave to look after their baby Alia. This meant Alia could be close by in Canberra, making it possible for Waters to combine her Senate work with breastfeeding.

"We need our stay-at-home dads to be more loud and proud," she says.

Obviously, recovering from birth and breastfeeding (if that's happening) makes it necessary for the mother to take some time off work. And each family's circumstances are different. But opening up ideas around who can be the primary carer doesn't just help mum's career and future earnings, but dad's relationship with the kids (don't take my word for it: the OECD says so, too).

Ardern and Gayford have been quick to concede they are not the first couple on earth to have a baby. They also note plenty of other families deal with work and home lives all the time. But as modest as they are, it's highly unusual for people to do it in on such a big stage.

Many women will be watching Ardern closely over the coming months, silently cheering her on as she negotiates two important, often competing identities. But we should also be cheering for Gayford, who will face his own challenges, looking after a new and growing baby – and hoping his experience can blast the message that men can be primary carers. Just as much as women can be prime ministers.