When it comes to getting paid, becoming a mother is a big drawback.
The average wage gap between men and women may be shrinking slowly, but new research in the U.K. shows it widens significantly after the birth of a child.
Twelve years after giving birth for the first time, women are making 33% less per hour than men, according to research by the Institute for Fiscal Studies.
On average, women in work receive about 18% less per hour than men. That's down from 23% in 2003.
The wider gap for mothers is not because women see an immediate cut in hourly pay after childbirth.
Possible explanations include mothers missing out on promotions or accumulating less labor market experience, the authors said.
The study found that by the time their first child is aged 20, women have on average been in paid work for four years less than men.
"Comparing women who had the same hourly wage before leaving paid work, wages when they return are on average 2% lower for each year spent out of paid work in the interim," the IFS said.
Related: Gender gap in U.S. Open ticket prices narrows
The IFS also found that the pay gap between highly educated women and men has not closed at all in 20 years, and remains stuck at just over 20%.
A separate study published by the Chartered Management Institute on Tuesday found that women are still missing out on promotions.
Related: Top U.K. investor scraps 'ineffective' bonuses
The survey of 60,000 managers in the U.K. showed that male managers were 40% more likely to be promoted compared to their female colleagues. The study also showed fewer women can expect a bonus -- 36% compared to 43% of men.
