As women fight what has been an uphill battle for equal pay, they continue to face another exacerbating factor: being penalized for the fact that they could — regardless of whether they will — have children.

While much of the public discussion of the "wage gap" has focused around women getting equal pay for the same work as their male peers, this quiet “pregnancy penalty” has gotten less attention, in part because it's so much more difficult to measure. But some experts argue that even the mere possibility that a woman can have a baby can be enough for employers to push her to the back of the line.

Women already know that announcing their pregnancy in the workplace will likely mean changes, said Katharine Zaleski, cofounder and president of PowertoFly, which connects women to positions that allow them to work remotely.

“A lot of women feel like, if they don't keep it under wraps, they’re going to get taken off projects that they'd been spending months, if not years working towards,” said Zaleski, who co-founded her company after becoming a mother. Expectant women are simply “cut out of the conversation,” she said.

Read More: Fan Influx Hasn't Bridged Soccer's Alleged Gender Wage Gap

Zaleski, now mother to a two-year-old, worked in digital media management for 15 years, at companies such as the Washington Post, NowThis, and Huffington Post. She said she’s seen “baby discrimination” affect many of her colleagues in various industries.

She recalled one incident in which a close female friend, who had a received a promotion, was told by a male colleague that he was not worried because he would “move past her by leaps and bounds” if she had a baby. “That’s the sort of mentality we're dealing with,” she said.

Taking median earnings of women and men who worked full time, year-round, government data from 2014 show that women make $0.79 for every dollar a man earns. The average earnings for working mothers come out to even less — $0.71 for every dollar a father makes, according to a 2014 study conducted by the National Partnership for Women and Children.

In a 2013 study, Mary Ann Mason, professor and co-director of the Center for Economics & Family Security at the University of California Berkeley School of Law, revealed some alarming outcomes for women in academia: Women graduate students who are pregnant or mothers with young children are 132 percent more likely to be working in a contingent position, while men with a young child are 36 percent less likely to be in a contingent position. Contingent positions are non-tenured, adjunct, or temporary jobs that are not secure.

That’s why female graduate students think twice about children, said Mason. They recognize the potential damage to their careers.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

“It's rather a brutal world. No one ever says this, but they will drop you from a project, or, if you take any kind of maternity leave, you will return to the backfield if you've been in front before. For other professions it's really quite similar,” said Mason.

“In fields like science, scientists are very nervous about having pregnant women because science is a big competition. You have to get there first. If you feel you have someone that is not going to be a hundred percent hitter, you are not going to keep them up front,” she said.

Read More: President Obama Announces Rules for Closing Gender Pay Gap

“It is often the case that mothers are held to a higher standard than others in the work place,” said Emily Martin, general counsel with the National Women’s Law Center. “And they are penalized if they cannot meet that standard.”

This higher standard is due to an antiquated notion that women who are pregnant are perpetually pre-occupied with their babies and cannot possibly be productive, said Anne-Marie Slaughter, author and former director of policy planning for the U.S. State Department.

“Pregnant women and mothers are assumed to be less committed to their careers, and every time they leave the office or ask for any flexibility, that commitment is further called into question," Slaughter said.

“This kind of discrimination is institutionalized,” said Lisa Maatz, a policy adviser with the American Association of University Women. “It’s a part of the culture, it’s a part of the decision-making process. Right now the assumptions about women's roles, as stereotypical as they may be, are driving decisions and those decisions disadvantage women.”

If there is one industry that seems to be handling the gender bias well, at least from a financial standpoint, it’s tech. In March 2016, tech career website Dice released a study of more than 16,000 tech professionals that found that when you compare equivalent education, experience and position, there is no pay gap — and hasn’t been for the last six years.

Dice’s director of communications, Rachel Ceccarelli, said one of the reasons behind fair compensation is supply and demand.

“Tech companies are scrambling for talent. They are looking for the best and brightest and realizing that if they want the best, they can’t eliminate half the population,” Ceccarelli said.

But the outlook isn't so sunny for everyone. Several studies have shown how women can lose out after a child is born, as well as how the hit to their careers can multiply as they have more kids. One such study, conducted by University of Massachusetts sociologist Michelle Budig, found that women lose about 4 percent in lifetime earnings per child.

Read More: Gender Pay Gap Will Be Erased, But It Will Take 118 Years, Report Says

That loss was totally unaccounted for by any external factors, like the woman working fewer hours or taking on more “family-friendly” jobs, Budig said. A possible explanation could be workplace stereotypes, she said.

“It seems to be the motherhood penalty increases as children age. It's not like you immediately get a lower paying job, but you miss out on the next promotion, you don't get the next raise, your performance is evaluated lower,” said Budig.

Even worse, it is almost impossible for women to counter the bias.

“Often, when you're the employee, you don't have a great window into what the employer bases decisions on. An employee does not have the data to challenge these sorts of decisions in many cases,” said the NWLC's Martin.

How pregnancy or the possibly of pregnancy is perceived in the workplace is potentially a problem for all women, said Heidi Hartmann, president of the Institute for Women’s Policy Research.

“A pregnancy penalty doesn’t just hurt mothers or expectant women, married women or even childbearing women, it’s a bias that's applied to all women,” said Hartmann.

“Nowadays employers probably don't think they're safe until that woman is [around] 49, but even then I don’t know."