Last year, after her second child celebrated her third birthday and started attending kindergarten, Dai went back to work, at a website that organizes playgroup activities.

"Now, I only need to work six hours a day. I feel very lucky to have found the job when I did," she said.

Huang, the professor, said motherhood can affect the time women can devote to work because health checks and other factors mean they have to take time off.

That makes them less efficient, and employers may not get value for money, which could even affect profitability. As a result, many employers prefer to hire men.

Moreover, competition in the job market has become fiercer, so companies do not like to hire younger women because they may need to take maternity leave, especially in the wake of the second-child policy, according to a Beijing Normal University report on the development of the labor market for women in China.