Many working women feel they are being pushed out of their jobs when they become pregnant while new fathers often get a boost in their careers, say researchers.
The findings, published in the Journal of Applied Psychology, confirmed inherent biases against expectant mothers that make them feel unwelcome in the workplace.
This is the first study to show that women who feel pushed out of the workplace choose to opt out, say researchers from Florida State University.
"We found that pregnant women experienced decreased career encouragement in the workplace only after they disclosed they were pregnant," said Paustian-Underdahl, assistant professor of Management.
"Once they told managers and co-workers, we saw a decline in career encouragement for women but an increase in career encouragement for men," she added.
To reach this conclusion, she studied two long-standing theories on why mothers are more likely to leave the workforce than fathers.
One suggests pregnant women feel "pushed out" of the workplace.
The second indicates moms decide for themselves during pregnancy to "opt out" because of changing personal and career values.
Known as the "motherhood penalty" and "fatherhood premium", researchers have attributed both to old cultural stereotypes that favour fathers as breadwinners and women as caregivers.
The findings indicate that as expectant moms receive reduced career encouragement at work, they experience lower motivation to stay with the organisation or in the workforce.
Fathers see the opposite effect. They get increased career encouragement from colleagues and managers and become more committed to their work.
The research offers new ideas on how to treat pregnant women.
"Primarily, workplaces should not reduce their career-related encouragement toward expectant mothers. In addition, managers should provide both fathers and mothers with social and career support to help them attain their work and family goals," said Paustian-Underdahl.