The different roles played by men and women upon becoming parents, with respect to paid work and childcare, are a crucial part of the development of gender pay gaps.

It is often argued that these stem from pre-existing gaps in earnings within opposite-gender couples – since men already earn a little more than women, on average, even before they have children – which drive decisions around who reduces paid work once children are born.

But new analysis from the Institute of Fiscal Studies shows that this divide occurs even when the mother had the higher wage in the household pre-childbirth – as is the case for 38 pe...