Since Monday, the political news cycle has been unusually preoccupied with pregnancy discrimination—specifically, an anecdote of Senator Elizabeth Warren’s. It’s one she returns to on the campaign trail—and one that likely feels all too familiar for many of the women listening.

As Warren tells it, she was fired from her first teaching job because she was pregnant: When she was six months along and visibly pregnant, the principal told Warren the job she had secured for the following year was going to someone else instead. The year was 1971—seven years before Congress passed legislation to outlaw pregnancy discrimination.

When I was 22 and finishing my first year of teaching, I had an experience millions of women will recognize. By June I was visibly pregnant—and the principal told me the job I’d already been promised for the next year would go to someone else.

— Elizabeth Warren (@ewarren) October 8, 2019

But this week, right-leaning media outlets called into question Warren’s claims, citing a 2007 interview that characterizes the experience differently and a transcript from a 1971 school board meeting obtained by the Washington Free Beacon, which indicates Warren’s teaching contract was extended.

In an interview with CBS News, Warren stood her ground, noting that she had been hiding her pregnancy and the board decision preceded her termination. “I was pregnant, but nobody knew it,” Warren told CBS News. “And then a couple of months later when I was six months pregnant and it was pretty obvious, the principal called me in, wished me luck, and said he was going to hire someone else for the job.” In interviews with retired teachers from Warren’s school, CBS News found that there was an unspoken rule at the time that female employees should see themselves out about five months into their pregnancy.

The doubt cast on Warren’s story may be politically motivated, but it also exemplifies why pregnancy discrimination—not unlike sexual harassment in the workplace—is so often dismissed. Those who haven’t experienced pregnancy discrimination firsthand may not recognize how insidious it is, even four decades after the passage of the Pregnancy Discrimination Act.

Even when people take their employers to court, it can be hard to provide incontrovertible evidence that an employer’s actions were the result of pregnancy discrimination. A lawsuit filed against retailer Nasty Gal in 2015, for example, alleged targeted layoffs of three pregnant employees and a male worker who was about to take paternity leave. But the company argued that those terminations coincided with a company restructuring and wider round of layoffs.

It’s easy, then, to spin a narrative that women are voluntarily leaving the workplace or stepping down the ladder, rather than responding to systemic barriers that make it harder for them to advance.

There’s ample data on the reality of pregnancy discrimination. In fact, the number of claims filed with the EEOC has climbed steadily over the last two decades. (Recently, for instance, a former Google employee filed a complaint over allegations of pregnancy discrimination.) According to the National Partnership for Women & Families, nearly 31,000 claims of pregnancy discrimination were filed with the EEOC and state employment agencies from 2011 to 2015.

Of those claims, almost a third were complaints from women who were allegedly fired for being pregnant. The other common complaints were more subtle, characterized as harassment or “discriminatory terms and conditions of employment.” Tens of thousands of women have reportedly taken legal action over pregnancy discrimination at major companies like Walmart, AT&T, Whole Foods, and 21st Century Fox.

Where it gets knotty is that in some scenarios, pregnancy necessitates special treatment and is comparable to a temporary disability under the law. But in other cases, special treatment can qualify as discrimination. As the EEOC notes, the Pregnancy Discrimination Act bars pregnancy-related discrimination around “any aspect of employment, including hiring, firing, pay, job assignments, promotions, layoff, training, fringe benefits, such as leave and health insurance, and any other term or condition of employment.” In jobs that require manual labor, if an employer denies a pregnant employee’s requests for shorter shifts or a lighter load, the outcome can be fatal. And a low-wage worker could get fired immediately after disclosing a pregnancy.

But in the corporate world, the bias can be more nebulous: It might manifest as being passed over for a promotion—steered onto the “mommy track”—or a boss scaling back a pregnant employee’s responsibilities. The discrimination need not be endemic to the industry or even company; it could be specific to one department, or one boss. Some companies may seemingly offer generous benefits but quietly discourage employees from taking advantage of those benefits. And then there are the instances of discrimination that keep people out in the first place—say, when a potential employer opts not to hire someone who’s pregnant.

was reminded today of an piece of advice most academic women heard before going on the job market:

“make sure and have a glass of wine at dinner so they know you’re not pregnant”

— Anne Helen Petersen (@annehelen) October 9, 2019

These sort of allegations aren’t as easy to peg as pregnancy discrimination, especially in a court of law, given the myriad reasons an employer could use to explain away their actions. In a 2015 case involving a woman whose job offer was rescinded after she disclosed her pregnancy, the Minnesota Supreme Court ruled that she lost her job not because she was pregnant, but because she then requested 12 weeks of unpaid maternity leave that she wasn’t legally owed. (This was despite evidence that her employer jotted down “Pregnant?” on her application.)

There is no singular experience of pregnancy discrimination. Even women who aren’t explicitly discriminated against for a pregnancy may be penalized by employers for the possibility that they might one day get pregnant or, upon having children, may be less committed to their work. We needn’t look further than the responses to Warren’s tweet to survey the intractable problem of pregnancy discrimination—and its contradictions and complexities.

I was fired the day after notifying of my pregnancy. And was told it was because “I wasn’t likeable enough”. I got a lawyer and a settlement.

Interviewing in the third trimester is an experience I wouldn’t recommend (albeit necessary for many)

— Emilia Merchen (@millypontipee) October 8, 2019

I can totally relate to this. I was fired in 1996 when I was five months pregnant, supposedly because work was “slowing down,” but actually for being pregnant. I know this because they called two weeks later in a real bind because they couldn’t keep up. Love me some #Karma.

— JustXie (@HnaXie) October 8, 2019

I learned I was pregnant on the first day of a new job in 1980. I shared the good news with my new boss and was unemployed within 4 hours, even though I was thoroughly qualified. Didn’t tell my next employer until I was showing at 4 1/2 months.

— Sharon McGee (@semcgee725) October 8, 2019