A new report from Zety found 75% of working mothers in the UK said becoming a parent hurt their careers.
Most mothers changed career paths or turned down promotions for flexibility.
84% said they feared telling their boss about being pregnant.
40% of mothers turned down promotions because of childcare, and fewer than one in five returned to full-time work after maternity leave.
Nine in 10 mothers said flexibility was their top priority at work.
One in five mothers said they faced harassment or negative comments for pregnancy or asking for flexible work.
45% of pregnant women reported being made redundant or excluded from projects.
11% of mothers lost their jobs due to pregnancy or maternity-related discrimination, which is about 54,000 mothers every year.
Most mothers who returned to work after maternity leave, around 86%, stayed with the same employer, but many found workplace support was lacking.
Roma Kończak, career specialist at Zety, said: “Behind every romanticised ‘simple life’ caption is a complex reality for working mothers.
“Flexibility becomes the top priority after motherhood, but the trade-off is steep: missed promotions, slower growth, and in some cases, stepping out of the workforce entirely.”