(NYTIMES) - As if working mothers did not have enough to worry about, experts are sounding the alarm that progress towards gender equality may be the latest in a long list of casualties of the coronavirus pandemic.

Substantial research has shown that most professional gender gaps are motherhood gaps; women without children are much closer to parity with men when it comes to salaries and promotions, but mothers pay a large career penalty.

Women tend to take on more of the burden of caring for children and the family.

To go to work, they need someone to help with that care. But fathers have been slow to change their behaviour. And without subsidies, private childcare can be prohibitively expensive.

Workplaces already tend to penalise women who choose to work fewer hours or need more flexibility, and that, too, is proving to be exacerbated in the pandemic.

"The bottom line is that, based on decades of research, we know that there was one institution that was effective at limiting gender inequality and encouraging women's participation in the workplace, and it was early childhood education," said economist Claudia Olivetti from the University of Chicago.

Now the pandemic is taking that away, too, piling pressure on working mothers.

Around the world, working women are facing brutally hard choices about whether to stay home if they have not already been laid off.

And the effect may be particularly severe in countries like the United States, where the pandemic is compounding inequalities that women already face as a result of the lack of guaranteed paid maternity leave and affordable childcare.

Israel is an example of the power of subsidised childcare to narrow gender gaps at work as well as a cautionary tale about how easily the pandemic can shatter that fragile progress.

The Israeli government provides free early childhood education from the age of three and means-tested daycare for many babies and younger toddlers.

Before the pandemic, women's overall labour force participation had reached 74 per cent, significantly higher than the Organisation for Economic Cooperation and Development average of 66 per cent.

The gender wage gap, though persistent, was narrowing.

Then came Covid-19. Schools and daycare centres closed in mid-March, and the childcare that had allowed so many mothers to work was gone.

Women already held more precarious positions in the workforce - working fewer hours, for less money, with shorter tenures and in lower-ranking jobs than men.

The loss of childcare limited many working mothers' hours and availability even further, meaning they were often the first to be selected for layoffs and unpaid leave.

And many families appear to be deciding that if they need one parent to give up a job and prioritise childcare, it should be the lower-paid parent - usually the mother.

Before the pandemic, many American mothers were effectively forced to stop working for some period of time because they could not afford paid childcare.

And research shows that the longer a woman is out of the workforce, the more severe the long-term effects on her earnings will be.

A 2018 study by the Institute for Women's Policy Research found that an employment gap of four years or more leads to a whopping 65 per cent cut in annual earnings, compared with a 39 per cent decrease after a one-year break.

As school closures force women out of the workplace for a year or two more than planned, that will have lifelong consequences for their financial stability.

A July report from McKinsey Global found that in the US, where women made up 43 per cent of the workforce, they accounted for 56 per cent of Covid-19-related job losses.

By contrast, Sweden, which heavily subsidises child daycare and has one of the highest rates of female labour participation in the developed world, has kept schools and daycare centres open throughout the pandemic.

Although this has been questionable as a public health strategy, it has allowed working parents to avoid the burdens of lockdown.

As with most social phenomena, this plays out differently for wealthy women than for poor ones.

Research shows that when high-earning couples have children, they tend to divide responsibilities.

With one parent stepping back from a career to take on the increased care duties, and the other making work a priority, it is usually the mother who steps back.

Once on the "mummy track", women make less money and have fewer opportunities for advancement. "If the woman is the secondary earner, then it is less costly at the margin to cut her hours" when a crisis like the pandemic hits, Dr Olivetti said.

Poorer families tend to have more parity between the parents' earnings, but they rely on both incomes to survive and are also more likely to have jobs that must be done in person rather than remotely. When schools and daycare centres close, there is no one to look after young children or supervise older ones' remote schooling if both parents go out to work.

But if one stays home, the family faces financial catastrophe.

"Trying to help working families ease this childcare constraint - it's not just a gender inequality issue; it's also an income inequality issue," Dr Olivetti said.

In short, the loss of school and daycare is going to set women back by 10 years because the only way for them to improve their public participation is by reducing the extra burden of caring responsibilities they have.