Many mothers face a significant loss of career status and pay when taking up part-time roles, new reports claim.
The birth of a first child is the primary factor in women choosing to work part-time
The talents of the UK's most qualified women are being wasted owing to "occupational downgrading" when they return to work.
Hourly earnings are 26% lower for women working part-time rather than full-time, says research in the February issue of the Economic Journal.
Six million women, 40% of those in work, are in part-time jobs.
"This loss of career status with part-time work is a stark failure among otherwise encouraging trends for women's advancement," said Sara Connolly and Mary Gregory, authors of one of the four reports.
"Girls and young women are outperforming males at all educational levels. They are moving into an expanding range of occupations, and building successful careers. The gender pay gap is narrowing.
"But for many all this comes to an abrupt halt when childcare claims part of the working week."
Impact of children
Some 85% of working women without children work full-time in Britain, according to an analysis of 84,000 interviews from the British Household Panel Survey by academic Gillian Paull.
That falls to 34% of working mothers with pre-school children and 41% of mothers with a youngest child of school age.
More than 90% of all working men, whether fathers or not, are employed full-time.
The pay gap between part-time and full-time work has been widening steadily over a number of years, one report claims, as part-time jobs are predominantly found in low-paid occupations.
'Hidden brain drain'
It goes on to say that almost a half of women managers of shops, salons and restaurants return after having a child to a less-skilled job with fewer responsibilities. This is more prevalent than other sectors, such as teaching and nursing.
Other reports published in the Economic Journal say that the UK has the worst part-time pay penalty - the difference of hourly rates for part-time and full-time working women - than the rest of Europe.
One report on job satisfaction suggests women with children are significantly happier if they have a job, regardless of the hours it entails.