Women who return to work after having a child continue to earn less than their male counterparts for years afterwards, according to a new report.
The wage gap consistently widens for 12 years after the first child is born, where women receive 33% less pay per hour than men, says the report by the Institute for Fiscal Studies (IFS).
Women who work half-time after giving birth lose out on wage progression, meaning the hourly wages of men continue to grow further ahead.
Those who take time out of paid work altogether after having a child and then return to work also miss out on pay growth.
Shainaz Firfiray, assistant professor at Warwick Business School said: "Women may take long breaks from work to attend to childcare responsibilities, but long periods away from work reinforce the notion that mothers will have discontinuous careers.
“Employers may be less inclined to invest in the training and development of employees who take long breaks and may allocate women to less challenging jobs post childbirth”.
IFS also said that that hourly wages of women working half-time or less appear to only change in line with economy-wide wages, meaning they don’t benefit at all from increased experience within the labour market.
Ms, Firfiray added: "Another reason women lag behind in pay levels is due to the fact that motherhood is perceived as a characteristic that is incompatible with the notion of the ideal worker.
“Higher acceptance of maternal employment and flexible work options may increase the prevalence of fairer practices in pay and promotion, and thus begin to tackle the gender inequalities that continue to disadvantage women."
Highly educated affected most
For those who are highly educated, the gender gap has remained relatively the same as it was 20 years ago.
Among the lowest-educated, those will less than A-levels, the gender gap has been steadily declining.
In 1993, the gap in average hourly wages was 28%, which then reduced to 23% in 2003.
This compared with the current wage gap of 18%.
Robert Joyce, associate director at IFS, said: “The gap between the hourly pay of higher-educated men and women has not closed at all in the last 20 years.
“The reduction in the overall gender wage gap has been the result of more women becoming highly educated, and a decline in the wage gap among the lowest-educated”.
Mothers employment rates drop by 33% for those with GSCEs, 19% for those with A-levels and 16% for graduates, whilst rates hardly drop at all for men.
New research by Citizens Advice also highlighted the amount of mothers facing discrimination at work for taking maternity leave. The study revealed a 50% increase in the number of maternity leave issues being brought to them face-to-face in the last two years and a 100% increase in online visits to pregnancy discrimination advice pages in the past year.
Citizens Advice said that the main issues new mothers faced were being made redundant, having hours reduced, lacking health and safety protections and having roles changed upon the return to work.
Earlier this year, the government announced that employers with more than 250 staff will have to reveal the number of men and women in each pay range and demonstrate where the pay gaps are at their widest. The plans are set to start in 2017.