A quarter of all mums feel discriminated against for having a baby, and half feel that giving birth halts their career progress. But Laura Bates argues that closing the door on so much talent disadvantages us all

"I went for a job near London Bridge and was told: 'We try to avoid hiring women as they have a nasty habit of getting pregnant and going off on maternity leave.'" "Myself and my female business partner were turned down for a contract last week as we're too much of a 'pregnancy risk'." "I have just been told that the reason my post has never been made permanent is the spectre of maternity leave. I have been in the post 16 years with no employee rights, which my male colleagues all enjoy."

These are just a few of the horrifying stories shared on the Everyday Sexism Project website by women who have experienced maternity discrimination. They are the kind of tales that are often brushed off or downplayed, particularly by those who believe that the equality laws in place should be sufficient to have wiped out any such prejudice years ago. But, as a new survey released by Mumsnet showed this week, the reality is very different.

As part of its Family Friendly initiative, the parenting website conducted a survey specifically focusing on the experiences of mums returning to work after having had a baby. They found that fully three quarters of respondents found it harder to progress in their career afterwards. Nearly a fifth (17%) said that their manager or employer was not supportive during their pregnancy and a quarter felt unsupported on returning to work.

And these figures are not unusual: a stark survey of 2,000 mothers by law firm Slater & Gordon in August this year revealed similar results. That survey found that a quarter of all mums who had returned to work after having a baby felt they had been discriminated against. Nearly half felt having children halted their career progression, and a third described continuing to rise up the ladder after becoming a mum as "impossible".

The thing about maternity discrimination is that it can be so much broader and more varied in its impact than many people imagine. It isn't just a case of having a bit of a tough time during your maternity leave and then going back to normal afterwards. In fact, incredibly, it isn't even something that is restricted to having an impact on parents; lots of women have reported being overlooked for promotion or grilled about baby plans at interview merely on the basis of their age and sex, when they had absolutely no intention of starting a family any time soon, or indeed, in many cases, at all! Several women described their pain at experiencing career discrimination on the basis of being a "pregnancy risk" when, in fact, they knew all too well that they were unable to have children.

For many women, there is a clear and immediate negative impact on their career from the moment of announcing their pregnancy …

"While pregnant, I was told by ex-boss I should resign. He said he couldn't plan around me having another baby in the future. And when I took it to HR, I was told he was 'probably just thinking out loud'."

For others, the impact is more subtle, as they return to work to find they have missed the opportunity to apply for a promotion, have been sidelined into a less senior position, or are simply treated very differently by their colleagues and managers.

"As I walked into the office … the first question asked by a more senior male colleague that I would be working for, was: 'Hi, so who is looking after your baby?'" "That afternoon another senior colleague thought it was acceptable to ask whether I would be properly involved in the new project, as 'women are not as committed to work after they have a baby'. He has three children but apparently the commitment only affects women …"

For women who are ready and eager to get stuck back into work, accusations of "baby brain" and "leaky nipples" are shockingly common, and incredibly frustrating. It is difficult to imagine new fathers putting up with similar assumptions about their reduced mental capacity. But many men are adversely affected by these strict, assumed gender roles as well; they reported difficulty in gaining time off for paternity leave, often facing the accusation from employers that they were somehow weak or less committed to their job for wanting to do what is so frequently seen as "women's work".

The crucial thing to realise here is that this is bad news for all of us. As hard as it might be to believe there are still people who,when these stories surface, rant angrily about the apparent selfishness of women getting themselves pregnant and then "expecting their employers to bear the financial burden". Reality check: women don't get pregnant by themselves, and like it or not, furthering the human race is in all our interests. As a necessary part of society, it is logical and fair that the cost of enabling this process to happen should be spread across society, and that means everybody playing their part. When we lose out on a large section of the workforce (the Equal Opportunities Commission found that 30,000 women are forced out of their jobs every year in the UK as a result of pregnancy discrimination) we are all disadvantaged as a result. Studies consistently show that greater diversity on boards leads to more successful business outcomes, so it is in all our interests to work together to end this discrimination that prevents some of our best and brightest from continuing in their careers, whether through shared parental leave or flexible working time.

We must tackle this problem head on, but in order to do so, we first have to acknowledge that it really does exist.