Margaret Lynch, an emergency room doctor, said she was told when she was hired that she would eventually be offered an ownership interest in the practice that supplied the facility's doctors.

She kept the same hours as the other doctors and became the emergency room's assistant director.

But after her complicated second pregnancy, she said, she was offered a smaller stake than the male doctors -- and only after she pushed them for it.

"I was told in March 2000 that I was not going to get partnership based on the fact I had gone on bed rest with the pregnancy, and they were afraid I might become pregnant again in the future," she said.

So Lynch, like a growing number of women, filed a complaint with the Equal Employment Opportunity Commission, claiming she was discriminated against based on pregnancy.

Pregnancy discrimination claims filed with the EEOC claims have risen 33 percent in recent years, to 4,512 in 2004 from 3,385 in 1992. Some of that increase reflects a growing number of women working during and after their pregnancies, but not all of it. During the same period, the percentage of working women with children younger than 18 rose by 5.2 percent.

"I think women are finally coming forward in larger numbers to say, 'I have a right to have a job and a family, and I'm not going to take it,' " said Elizabeth Grossman, acting regional lawyer for the EEOC in New York. As a result, pregnancy complaints have become one of the fastest-growing classes of charges filed with the EEOC, just behind religion and national origin, despite the fact that the Pregnancy Discrimination Act has been on the books since 1978.

Grossman said instances of discrimination have not necessarily increased. Rather, the number of women willing to fight back has grown.

Grossman's office recently sued and won a settlement for a waitress who was removed from a managerial career track, denied work assignments and told to "consider her options" after she revealed she was pregnant. Ultimately, she was fired. The woman received $145,000 in a pregnancy discrimination settlement with her former employer.

"The stereotypes continue, and employers need to focus on this issue and train managers appropriately and take a good, hard look at their policies," Grossman said.

Since the case settled last year, Kam Wong, the EEOC attorney who handled the case, said her office has filed three similar actions.

Debra Ness, president of the National Partnership for Women & Families, said women are increasingly unwilling to accept setbacks resulting from bias. She said she is seeing many more cases of pregnancy discrimination, where women are being "sidelined, not getting great assignments, passed up for promotions, raises." The cases "range from harder to define things to really being either forced out of your job or receiving unsubstantiated disciplinary action," she said. In the most egregious, "women start to get bad reviews when there is no basis."

"Women are usually so terrified to tell their boss" about a pregnancy, said Mary Jo O'Neill, a regional lawyer for the Phoenix EEOC. "And why is that? It's because pregnancy discrimination is an epidemic out there." She said there has been a 182 percent increase in pregnancy discrimination charges filed in Arizona in the past decade.

O'Neill attributed the increase to a "knowledge vacuum." She said that companies train new hires to avoid sex discrimination and harassment but do not mention, or may not know about, pregnancy discrimination.

Dana Law, an organizational psychologist and human resources consultant, said that when she works with clients, pregnancy discrimination is not explicitly stated unless it is part of a discussion about the Family and Medical Leave Act. Pregnancy discrimination is "still a problem, because people don't know or aren't aware that it's illegal to discriminate on the basis of that," she said. "When you have an increasing number of women entering the workforce and fewer numbers of managers that know, of course the claims are going to rise."

One of those claims includes an auto service technician O'Neill's office represented, who was fired soon after telling her boss she was pregnant.

Mailyn Pickler, the technician, was nervous to tell her boss after she found out she was pregnant but thought she should do it as soon as she finished her first trimester. Her boss, according to the suit, told her he was afraid she would vomit while driving the company's shuttle bus.

According to the complaint, the boss at the auto care center in Mesa, Ariz., indicated that she would be rehired in her job as a general service technician after she completed her pregnancy, provided she produce medical evidence of a complete physical recovery. The case was settled last year for $70,000.

"I knew something was wrong. I just thought, 'They can't fire you because you are pregnant,' " she said. She recently had a second child and is not working outside the home now, but is attending school.

Lynch, the doctor whose case is still pending, waited for the partnership to "come to its senses," she said. But after she complained, she said, she was demoted and the partnership offer was revoked.

Lynch's former employer said the claim has no merit and that she was offered more equity than male colleagues, but that she turned the offer down. Lynch said she was offered substantially less than originally promised and that her pregnancy was cited as a factor.

She now works at a different emergency room and is the mother of four children ages 2 to 8, with another child on the way.

Another case, which expands a sex discrimination claim to include pregnancy and caregiver discrimination, was filed in May as a private class-action case against the biomedical firm Novartis.

The suit, filed on behalf of 12 women who claim the company has a pattern of discriminating against women, says women employees were demoted or fired after they announced they were pregnant or after they returned from maternity leave.

"A growing number of women are coming forward who speak about doing well at work and being on a career path and competing successfully at the workplace. And then discovering that they're pregnant, announcing that they are pregnant and may take pregnancy leave and suddenly have everything change. What was once a very promising career and career path suddenly turns into a brick wall," said David W. Sanford, a Washington lawyer representing the women.

Karen Sutherland, a Novartis spokeswoman, said the company disagrees with all the claims and looks forward to presenting its side of the case in court. She said that for seven consecutive years, the company has been recognized by Working Mother Magazine as a top place to work.

"You have this volatile combination of Generation X and Y women feeling entitled to be in the workplace and live up to widely held ideals of motherhood," said Joan C. Williams, law professor and director of the Center for WorkLife Law at the University of California, Hastings. "And employers who simply appear not to know that it's gender discrimination to push them out."

Margaret Lynch, with son, Ryan, filed a bias claim with the EEOC, which says pregnancy complaints are one of the fastest-growing classes of charges.

Margaret Lynch with children Maureen, left, Clare, Mark and Ryan. Lynch filed a complaint with the EEOC, citing pregnancy bias.