Every year, 30,000 women are sacked or forced out of their jobs because of pregnancy and 200,000 more face discrimination, according to the Equal Opportunities Commission.
By Martin Small
BBC Money Programme
Ms Boulton lost her job and her £129,000 salary
All this is 30 years after the introduction of laws which made such practices illegal, and which were supposed to safeguard pregnant women in the workplace.
It happens to women in all kinds of jobs, from the lowest paid to the highest.
Take Chanine Boulton, who earned £129,000 a year as one of Canon UK's top photocopier salespeople.
When she had her daughter Layla in 2003, everything seemed fine.
But while she was away on maternity leave, Canon reorganised its sales force - without telling Chanine.
Her best accounts, which generated most of her income, were given to a male colleague. She felt she had no choice but to quit.
"I hadn't done anything wrong," Ms Boulton says.
"They had no reason to treat me like this. They had obviously written me off."
Not just a job
At the other end of the income scale is Sarah Taylor, who earned £14,000 a year as a supervisor for Cablepoint, a small engineering firm in Hull.
Ms Holland wonders whether her education has been wasted
In 2002, she suffered a miscarriage late in her pregnancy, but then quickly became pregnant again.
First she had to endure insensitive remarks about her bereavement by her manager.
Then, after she gave birth to her daughter Georgia, her employers refused her request to work part time.
She resigned, feeling that she had been pushed out of a job she loved.
"It was everything I'd worked for and everything I'd wanted to do" Ms Taylor says.
"To other people it was just a factory job. But to me it was my life."
Forced to move
This kind of discrimination can affect not just women, but their whole families.
Sarah Holland was a software developer for a small firm in London, Information Initiatives, where she earned £29,000 a year.
But immediately after she discovered she was pregnant with her son Luke, she was made redundant.
With their income down by two-thirds, she and her husband Dave could no longer afford to stay in their house, and had to move.
"There was no central heating, no double glazing, no hot water system" says Ms Holland.
"My son was very ill because we moved in there coming up to winter, so it was extremely cold and he got chest infections.
"And having to move your child into that environment, you feel like a failure as a mother."
All three women took their cases to employment tribunals and were found to have suffered unfair dismissal and sex discrimination.
But few follow a similar path.
Of the 30,000 women who lose their jobs each year due to pregnancy, only 1000 go to a tribunal.
"These are women who are pregnant or who have just had a baby. Really their first focus is not standing up in court and doing a Perry Mason," says Victoria von Wachter, a leading employment barrister.
And even if women can afford expensive lawyers, or have the backing of a union, going to tribunal can be daunting.
"The complexities of the legal points that are now being argued are breathtaking compared with 30 years ago" says Ms von Wachter.
The complexities of the laws concerning maternity in the workplace may help explain some of the apparent discrimination, according to some businessmen.
Steve Noble, a partner in a Bristol-based public relations firm, Publicity Matters, says that smaller companies have to cope with too much red tape.
"Most small businesses spend their time trying to evade regulation rather than actually working with it," Mr Noble says.
"In the end it's tempting just to dump the lot and just muddle through."
But when employers ignore the law and get rid of staff simply because they want to have a child, the consequences can be devastating.
Ms Holland believes that having been out of work for over 2 years now she has lost more than just a job.
"I think effectively my career is over," she says.
"To have it all taken away so abruptly is hard, and you wonder... if all the education you went through was worthwhile."
The Equal Opportunities Commission and charities like Tommy's can provide help and advice on the issues raised in this story. The Forum of Private Business publishes an online guide to employment law. For more information go to the internet links at the top of the story.
The Money Programme - Pregnant? You're fired! - BBC TWO at 7pm on Friday 25 November.