Women face a widening pay gap with men once they start a family, a study has found.
The Institute for Fiscal Studies (IFS) found that while the overall "gender wage gap" had narrowed over the past two decades, women with children are still falling behind.
What did the study find?
The study, carried out for the Joseph Rowntree Foundation, found that on average, hourly pay rates for women are currently around 18% lower than for men. That compares with a gap of 23% in 2003 and 28% in 1993.
However once women started a family, gap widened consistently year by year so that by the time their first child had reached the age of 12, their hourly pay was 33% down on men.
Why do women face a pay gap?
The report suggested the difference may be down to women working fewer hours once they have children and, as a consequence, missing out on promotions - or simply accumulating less labour market experience - while their male colleagues pull further and further ahead.
When are women affected the most?
It also found the closing of the overall wage gap was down to improvements in the pay rates of less well-qualified women, who did not have A-levels or other higher qualifications, while for better-educated women the gap had remained unchanged for 20 years.
IFS director Robert Joyce, a co-author of the report, said: "Women in jobs involving fewer hours of work have particularly low hourly wages, and this is because of poor pay progression, not because they take an immediate pay cut when switching away from full-time work."
What reaction has the report received?
TUC general secretary Frances O'Grady said: "It is scandalous that millions of women still suffer a motherhood pay penalty,
"Many are forced to leave better-paid jobs due to the pressure of caring responsibilities and the lack of flexible working."
Labour's shadow women and equalities minister, Angela Rayner, said: "It is unacceptable that the wage gap between men and women with 'A' levels or degrees has remained unchanged over the last 20 years."
A spokesman for the Equality and Human Rights Commission said: "We simply cannot ignore the true scale of the hidden discrimination that working mothers face. It is unacceptable in modern Britain that three in four working mothers say they experience pregnancy and maternity discrimination each year.
A Government spokesman said: "The gender pay gap is the lowest on record but we know we need to make more progress and faster. That's why we are pushing ahead with plans to force businesses to publish their gender pay and gender bonus gap - shining a light on the barriers preventing women from reaching the top."