Many pregnant women have been systematically sidelined in the workplace. They’re passed over for promotions and raises. They’re fired when they complain.

When she got pregnant, Otisha Woolbright asked to stop lifting heavy trays at Walmart. Her boss said she had seen Demi Moore do a flip on TV when she was nearly full-term — so being pregnant was “no excuse.” Ms. Woolbright kept lifting until she got hurt. When she got pregnant, Rachel Mountis was winning awards for being a top saleswoman at Merck. She was laid off three weeks before giving birth. When she got pregnant, Erin Murphy, a senior employee at the financial giant Glencore, was belittled on the trading floor. After returning from maternity leave, she was told to pump milk in a supply closet cluttered with recycling bins.

American companies have spent years trying to become more welcoming to women. They have rolled out generous parental leave policies, designed cushy lactation rooms and plowed millions of dollars into programs aimed at retaining mothers.

But these advances haven’t changed a simple fact: Whether women work at Walmart or on Wall Street, getting pregnant is often the moment they are knocked off the professional ladder.

Throughout the American workplace, pregnancy discrimination remains widespread. It can start as soon as a woman is showing, and it often lasts through her early years as a mother.

The New York Times reviewed thousands of pages of court and public records and interviewed dozens of women, their lawyers and government officials. A clear pattern emerged. Many of the country’s largest and most prestigious companies still systematically sideline pregnant women. They pass them over for promotions and raises. They fire them when they complain.

In physically demanding jobs — where an increasing number of women unload ships, patrol streets and hoist boxes — the discrimination can be blatant. Pregnant women risk losing their jobs when they ask to carry water bottles or take rest breaks.

In corporate office towers, the discrimination tends to be more subtle. Pregnant women and mothers are often perceived as less committed, steered away from prestigious assignments, excluded from client meetings and slighted at bonus season.

Each child chops 4 percent off a woman’s hourly wages, according to a 2014 analysis by a sociologist at the University of Massachusetts, Amherst. Men’s earnings increase by 6 percent when they become fathers, after controlling for experience, education, marital status and hours worked.

“Some women hit the maternal wall long before the glass ceiling,” said Joan C. Williams, a professor at University of California Hastings College of Law who has testified about pregnancy discrimination at regulatory hearings. “There are 20 years of lab studies that show the bias exists and that, once triggered, it’s very strong.”

Of course, plenty of women decide to step back from their careers after becoming mothers. Some want to devote themselves to parenthood. Others lack affordable child care.

But for those who want to keep working at the same level, getting pregnant and having a child often deals them an involuntary setback.

The number of pregnancy discrimination claims filed annually with the Equal Employment Opportunity Commission has been steadily rising for two decades and is hovering near an all-time high.

It’s not just the private sector. In September, a federal appeals court ruled in favor of Stephanie Hicks, who sued the Tuscaloosa, Ala., police department for pregnancy discrimination. Ms. Hicks was lactating, and her doctor told her that her bulletproof vest was too tight and risked causing a breast infection. Her superior’s solution was a vest so baggy that it left portions of her torso exposed.

Tens of thousands of women have taken legal action alleging pregnancy discrimination at companies including Walmart, Merck, AT&T, Whole Foods, 21st Century Fox, KPMG, Novartis and the law firm Morrison & Foerster. All of those companies boast on their websites about celebrating and empowering women.

Erin Murphy, with her sons, Wyatt, 3, at right, and Emrys, 13 months. She has filed a complaint of pregnancy discrimination with the Equal Opportunity Employment Commission against her employer, Glencore. Chad Batka for The New York Times

Women’s Brains

As a senior woman at Glencore, the world’s largest commodity trading company, Erin Murphy is a rarity. She earns a six-figure salary plus a bonus coordinating the movement of the oil that Glencore buys and sells. Most of the traders whom she works with are men.

The few women at the company have endured a steady stream of sexist comments, according to Ms. Murphy. Her account of Glencore’s culture was verified by two employees, one of whom recently left the company. They requested anonymity because they feared retaliation.

On the company’s trading floor, men bantered about groping the Queen of England’s genitals. As Glencore was preparing to relocate from Connecticut to New York last February, the traders — including Ms. Murphy’s boss, Guy Freshwater — openly discussed how much “hot ass” there would be at the gym near the new office.

In 2013, a year after Ms. Murphy arrived, Mr. Freshwater described her in a performance review as “one of the hardest working” colleagues. In a performance review the next year, he called her a “strong leader” who is “diligent, conscientious and determined.”

But when Ms. Murphy told Mr. Freshwater she was pregnant with her first child, he told her it would “definitely plateau” her career, she said in the affidavit. In 2016, she got pregnant with her second child. One afternoon, Mr. Freshwater announced to the trading floor that the most-read article on the BBC’s website was about pregnancy altering women’s brains. Ms. Murphy, clearly showing, was the only pregnant woman there.

“It was like they assumed my brain had totally changed overnight,” Ms. Murphy, 41, said in an interview. “I was seen as having no more potential.”

When she was eight months pregnant, she discussed potential future career moves with Mr. Freshwater. According to her, Mr. Freshwater responded, “You’re old and having babies so there’s nowhere for you to go.”

A Glencore spokesman declined to comment on Mr. Freshwater’s behalf.

After she came back from four months of maternity leave, she organized her life so that having children wouldn’t interfere with her career. She arranged for child care starting at 7 a.m. so she would never be late.

But as her co-workers were promoted, her bosses passed her over and her bonuses barely rose, Ms. Murphy said.

When there was an opening to be the head of her department, Ms. Murphy said she never got a chance to apply. The job instead went to a less experienced man. Ms. Murphy said an executive involved in the selection process had previously asked repeatedly whether she had adequate child care.

Ms. Murphy said that after she missed out on another job, the same Glencore executive told her it was because of the timing of her maternity leave. Ms. Murphy has retained a lawyer and is planning to file a lawsuit against Glencore.

Glencore’s spokesman, Charles Watenphul, defended the company’s practices. “Glencore Ltd. is committed to supporting women going on and returning from maternity leave,” he said. He said Ms. Murphy was never passed over for promotions or treated differently because of her pregnancies. He said that she received bonuses and pay increases every year. Her lawyer, Mark Carey, said that Ms. Murphy was only given cost-of-living increases and was denied opportunities to advance.

Ms. Murphy’s problems are not rare. Managers often regard women who are visibly pregnant as less committed, less dependable, less authoritative and more irrational than other women.

A study conducted by Shelley Correll, a Stanford sociologist, presented hundreds of real-world hiring managers with two résumés from equally qualified women. Half of them signaled that the candidate had a child. The managers were twice as likely to call the apparently childless woman for an interview. Ms. Correll called it a “motherhood penalty.”

“There is a cultural perception that if you’re a good mother, you’re so dedicated to your children that you couldn’t possibly be that dedicated to your career,” Ms. Correll said.

A paper published in November by researchers at the Census Bureau examined the pay of spouses. Two years before they had their first child, the husbands made only slightly more than their wives. By the time their children turned 1, the size of that pay gap had doubled to more than $25,000. Women taking maternity leave, dropping out of the work force or working fewer hours could contribute to that disparity, but it does not explain all of it, the researchers said.

Ms. Murphy still works at Glencore. In January, she filed a complaint of pregnancy discrimination with the Equal Employment Opportunity Commission. Last year, the agency received 3,184 pregnancy discrimination complaints, about twice as many as in 1992, when it began keeping electronic records. Regulators say many women never file complaints because they can’t afford an attorney, don’t recognize that what happened to them is illegal or fear retaliation.

Rachel Mountis, who is part of a lawsuit accusing Merck of paying women less than men and denying them professional opportunities, with son Max, age 7. Mike Belleme for The New York Times

Lost Momentum

Merck, the giant pharmaceutical company based in Kenilworth, N.J., presents itself as a champion of professional women. “We celebrate the women whose hard work and tenacity have helped us continue to invent for life,” the company’s website boasts.

That is part of the reason Rachel Mountis wanted to work there.

Within a year of joining in 2005, she was given a coveted job selling vaccines. She was promoted four years later. She won a Vice President’s Club Award for sales and a Peer Award for “outstanding leadership.” Merck paid for her to get a master’s degree in business at New York University.

Ms. Mountis knew that when she got pregnant in 2010 she would need to take several weeks off for maternity leave. That meant she wouldn’t be able to stay in constant contact with the doctors she had cultivated as customers — and that her absence could cost Merck business.

A few weeks before Ms. Mountis’s due date, Merck told her and a handful of colleagues that they were being laid off in a downsizing.

“On paper, I was the same professional that I was nine months earlier,” she said. Being pregnant “was the only thing that was different.”

Ms. Mountis eventually got another job at Merck, but it was a demotion with lower bonus potential.

Merck was already facing a lawsuit accusing the company of paying women less than men and denying them professional opportunities. That suit, in New Jersey federal court, was brought by Kelli Smith, a Merck saleswoman who said her career was derailed when she got pregnant. “You’re not going anywhere” at the company, a male colleague told Ms. Smith, according to the suit.

The women involved in the litigation say they were harassed by male superiors.

At a conference, a Merck executive referred to a female employee as the “hottest one in here” and asked what he could do to get her upstairs to his hotel room, according to court documents.

At another company event, the same executive referred to a group of women from a company that Merck had just acquired as “whores” and said “they are much hotter than the Merck whores.”

In 2014, Ms. Mountis joined the lawsuit, which now covers roughly 3,900 women.

A trial date has not been set. A Merck spokeswoman said the company “has a strong anti-discrimination policy.” Ms. Mountis, the spokeswoman said, “was supported throughout her career to ensure she had opportunities to advance and succeed.”

Ms. Mountis tried to make the best of her less prestigious job. Merck demoted her again in 2012, while she was on maternity leave after giving birth to her second child. The next year, Ms. Mountis resigned. She eventually took a job at a pharmaceutical company that is a fraction of Merck’s size.

“I am still trying to get my momentum back,” Ms. Mountis said.

Ms. Smith also moved to a much smaller drug company.

Other drug companies have faced similar complaints. Novartis in 2010 agreed to pay $175 million to settle a class-action lawsuit in which thousands of current and former sales representatives said the company discriminated against women, including expecting mothers, in pay and promotions.

One former Novartis saleswoman, Christine Macarelli, said that her boss told her that “women who find themselves in my position — single, unmarried — should consider an abortion.” When she returned from maternity leave, she said she was told to stop trying to get a promotion “because of my unfortunate circumstances at home — being my son Anthony.”

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Peggy Young, with her daughter Triniti, age 11. Ms. Young sued U.P.S. for discrimination after the company said it couldn’t give her a light-duty job when she got pregnant. The Supreme Court ruled in her favor in 2015. Gabriella Demczuk for The New York Times

A Feminist Revolt

The nation’s first law against pregnancy discrimination traces back to a 1970s case about how General Electric treated expectant mothers.

The company at the time gave paid time off to workers with disabilities, but not to pregnant women. The Supreme Court ruled in 1976 that the company’s policy wasn’t discriminatory.

Feminist leaders and unions campaigned to change the law to protect pregnant women. In 1978, Congress passed the Pregnancy Discrimination Act, which made it illegal to treat pregnant women differently from other people “similar in their ability or inability to work.”

That didn’t resolve the issue. Employers argued in court that pregnant women were most “similar” to workers injured off the job and, therefore, didn’t deserve accommodations.

Then, Peggy Young sued U.P.S. for discrimination. She had been an early-morning driver when she got pregnant in 2006. Her doctor instructed her not to lift heavy boxes. U.P.S. told her it couldn’t give her a light-duty job. She ended up on unpaid leave without health insurance.

Ms. Young outside the Supreme Court. During oral arguments in 2014, Justice Ruth Bader Ginsburg challenged UPS’s lawyer to cite “a single instance of anyone who needed a lifting dispensation who didn’t get it except for pregnant people.” The UPS lawyer drew a blank. Stephen Crowley/The New York Times

At the time, U.P.S. gave reprieves from heavy lifting to drivers injured on the job and those who were permanently disabled. Even employees who had lost their licenses after driving drunk got different assignments. Ms. Young argued that she should have gotten the same deal.

Two federal courts ruled in U.P.S.’s favor. Ms. Young appealed to the Supreme Court. During oral arguments in 2014, Justice Ruth Bader Ginsburg challenged U.P.S.’s lawyer to cite “a single instance of anyone who needed a lifting dispensation who didn’t get it except for pregnant people.” The U.P.S. lawyer drew a blank.

In 2015, the court ruled 6 to 3 in Ms. Young’s favor. But the justices stopped short of establishing an outright protection for expectant mothers. They just said that if employers are accommodating big groups of other workers — people with disabilities, for example — but not pregnant women, they are probably violating the Pregnancy Discrimination Act.

Otisha Woolbright, who has sued her former employer, Walmart, for pregnancy discrimination, with her children, clockwise, Kamilah, 8 years old; Ny’trinity, 11; Erick, 9, Jaia, 4; and Jacob, 7 months. Charlotte Kesl for The New York Times

Demi Moore’s Stunt

Otisha Woolbright heaved 50-pound trays of chickens into industrial ovens every day at her job in the deli and bakery of a Walmart in Jacksonville, Fla.

In 2013, when she was three months pregnant, she started bleeding and went to the emergency room. She was told that she was at risk of miscarrying. She returned to Walmart with a physician’s note saying that she should avoid heavy lifting. She asked for light duty.

That’s when her boss, Teresa Blalock, said she had seen a pregnant Demi Moore do acrobatics on TV.

In an email to The Times, Ms. Moore said that a stunt double actually performed the routine.

“You would have to be extremely ignorant and inexperienced with pregnancy or just completely uncaring and insensitive to use a moment of comedic entertainment, like my appearance on David Letterman while I was eight and a half months pregnant, to pressure a pregnant woman into doing something that put her or her baby at risk,” she said.

According to Ms. Woolbright, Ms. Blalock said that if she couldn’t lift chickens, she could “walk out those doors.”

Ms. Woolbright couldn’t afford to lose her paycheck, so she kept lifting chickens.

“What choice did I have? There was no other job that was going to hire me being pregnant,” she said.

Later that month, Ms. Woolbright said, she was lifting a tray of chickens when she felt a sharp pain. Scared she was having a miscarriage, she went back to the hospital. Walmart then put her on light duty.

“We disagree that a specific request for accommodations due to pregnancy was made and that we denied that request,” a Walmart spokesman, Ragan Dickens, said. He said that “Ms. Blalock, a mother and a grandmother, was supportive of Ms. Woolbright.”

Ms. Woolbright asked about maternity leave. Three days later, she said she was called into a cramped office. She stood there sweating, seven months pregnant. “Walmart will no longer be needing your services,” a supervisor said.

Ms. Woolbright sued Walmart, the nation’s largest employer. Her suit, which is seeking class-action status, is pending.

It took Ms. Woolbright a year to land another job. Her children outgrew their clothes. She thought about swallowing enough antidepressants to kill herself. After stints at a restaurant and a van rental company, she stopped working, because she couldn’t get shifts that allowed her to take care of her children.

Walmart is the least expensive store in town, and Ms. Woolbright goes there to buy baby formula and diapers. “It’s torture,” she said.

Candis Riggins, who says Walmart failed to reassign her when she was five months pregnant and became ill from cleaning products, with her children, from left, Jhazlyn, age 4; Jhayce, 6; and Jhadie, 8. Gabriella Demczuk for The New York Times

Pausing to Vomit

Seven hundred miles to the north, Candis Riggins was scrubbing toilets at a Walmart in Laurel, Md., when she started to feel sick. She was five months pregnant, and the smell of the cleaning fluids nauseated her. She complained several times to a manager, who refused to permanently reassign her to another position. So she kept cleaning bathrooms, often pausing to vomit.

Doctors told her that chemicals in the cleaning products were endangering her and her unborn child.

One chilly morning on her way to work, she fainted at the bus stop.

Ms. Riggins again asked a manager for a different job. This time, Walmart let her clean the store’s doors instead of the bathrooms. But she said the chemicals still made her ill.

She was eight months pregnant when she started regularly missing shifts. Walmart fired her, citing the absences. She now works at Target.

Mr. Dickens, the Walmart spokesman, said the company allowed her to stop working with the chemicals she complained about and occasionally let her work as a cashier or store greeter. Ms. Riggins’s lawyer, Dina Bakst, said that her client still had to spend most of her days cleaning.

In 2017, under pressure from Ms. Woolbright’s class-action lawsuit and E.E.O.C. complaints, Walmart updated its guidelines on how to accommodate pregnant women. The nationwide policy now includes a temporary, less taxing job as a “possible” solution. It doesn’t provide a guarantee.