It used to be assumed all women would marry and have children. But today, the Office of National Statistics estimates that a quarter of all women born in 1973 will remain without children – some by choice, others because it didn't work out.

Meanwhile mothers increasingly feel that parenthood has lost its status. Now it's an 'individual choice' – nobody's business but the parents. Motherhood, once the one unifying factor of womanhood, has become a dividing line in a war of lifestyle choices, on either side of which lurks misunderstanding, resentment and envy.

Mothers are tired of being branded smug, frumpy and unreliable at work. Women without children are sick of being characterised as glossy but selfish, hard-nosed career women or objects of pity, unable to understand the emotional rewards of motherhood. Mothers know they are resented for being less flexible, but are miserable because so few people seem to accept why this has to be, or how hard they work.

Women without children can feel hurt by the careless comments that mothers can make, such as 'you wouldn't understand, you don't have children'. They feel not having children is something they must explain or defend. The two are united in their sense of isolation and defensiveness, and are increasingly being set up to distrust or dislike each other. The more mothers feel isolated and undervalued, the more they try to insist on the importance of motherhood. The more women without children are portrayed as superficial and 'missing out', the more defensive and hurt they feel. How did it come to this?

'Some women without children are grieving'
RACHEL BLACK, 53
co-author of Beyond Childlessness (£12.99, Rodale)

There are some incredibly painful parts about not being a mother. Often there is a deep sense of somehow being 'less than' a real woman.
If you dreamt of having children and it hasn't happened yet, your hope is kept alive by news stories of late motherhood. But eventually you have to accept that it's probably not going to happen. It's horrific to start with, and can leave you with feelings of grief, loss and failure. Then you begin to think, 'if I'm not going to be a mother, what am I going to be?' It's a long road, but what lies ahead is up to you.

Some women without children are grieving; it's the loss of something that never was. And that can be hard for anyone else to understand and deal with sensitively. Often mums will say things like, 'you don't know how lucky you are'. They also tend to innocently ask whether you have children, which puts women without children on the defensive.
One of the most rewarding comments I've had is, 'that's a shame, you would have made a wonderful mum'. It's the opposite of saying anything that might imply that you're a selfish career woman. If you're a mother, society accords you a status, you're seen as maternal and nurturing; for women without children, you've got the 'career woman' slot, but not much else that is positive. You must create your own identity.

'Mothers despair of explaining what it's all about'
NAOMI STADLEN, 63
psychotherapist and author of What Mothers Do – Especially When it Looks Like Nothing (£9.99, Piatkus)

I don't believe mothers resent other women for not having babies, what they resent is being misunderstood. People ask things like, 'what on earth do you do all day?', or 'why can't you get a babysitter tonight?'. And what mothers say to me is 'I don't know how I can do it, how can I manage it all?' It's isolating. There's a despair of not being able to explain what it's all about. Yes, mothers may have to pack up work and rush home because the babysitter is leaving. But they may well have preferred to stay and finish off their work, and they feel resentful that their situation isn't understood.

People who resent mothers might view mothering as a 'hobby', but actually mothers are bringing up the next generation – it's their children who will be caring for us when we are old and feeble. In the long-run, you get the benefits. Ultimately, the birth rate is going down, so we need to support mothers.

'Parents think we don't understand'
ESTHER FREEMAN, 31
senior press officer at CSV Make a Difference Day, is in a long-term relationship, and has no children

One thing that used to get to me in my last job was the parents who had their little gang and would say things like, 'you don't understand because you haven't got kids'. It would really annoy me because I have experience of looking after my friends' kids and talk to enough parents to know that parenting is a hard job. I can empathise. I think that parents get a rough time, and many non-parents don't understand that when parents are off work to look after sick kids they're not out having fun, they're cleaning up vomit. But the way parents shut out non-parents doesn't help their cause.

'I had to deny my children's existence'
LINDSAY BOYERS, 50
a senior tax investigations manager, returned to work after having both of her daughters – one at 22 and the other at 40

When I had my first daughter I felt undermined by the 'career' women without children who seemed to have more choices than I did. They were competitive, and thought nothing of coming in at weekends – if I didn't, they would. My daughter suffered because I practically lived in the workplace, pretending she didn't impinge on my job. I couldn't even have her photos in the office.

After having my second child, I was told I wasn't up for promotion because having a small child may mean an inability to work 70-hour weeks. I gave my whole life to that job, denying the existence of my children, so to be told I couldn't go any further because I had a child made me so angry. Even now I'm still fighting for working mothers and pretending my daughter is not a bar to my career. Having a child in the 1970s felt like something you had to apologise for if you wanted a professional career. It's more acceptable now, but it's no easier.

'To be penalised for not having children is wrong'
CHARLOTTE HARPER, 35
managing director of Match.com, is six months pregnant with her first child

I got married last October and became pregnant very quickly. I wasn't actively trying, but at my age you hear so many horror stories about not conceiving. When the book Baby Hunger came out [about women leaving it too late to have children], I thought 'how dare these people prey on women's insecurities – that at the age of 35 your fertility is over?' It makes me so angry. I know how I felt as a single women reading that stuff – upset and panicky, and that's not a way to meet someone. In my experience, women aren't deliberately postponing having kids, they're often just trying to find the right partner. But they are labelled as ambitious and sacrificing children on the altar of ambition. To be penalised for not having children is wrong. We're either mothers or we're selfish – it's as if there is no in-between.

'I'm riddled with guilt'
ALEXANDRA OVERTON-WOOD, 39
a business development director, has one daughter

As a working mother, I sit in the middle. I feel guilty that I don't pick my daughter up from school enough and guilty at having to leave work on time when my colleagues without children are still glued to their computers. And I feel guilty about talking to a non-mother about my daughter – they probably don't want to know. Women without children get bored when their friends talk about their kids all evening. They can relate if you're talking about relationships, but your children aren't necessarily of interest.
To constantly juggle trying to be a great mother, partner, friend and employee is quite a challenge – I'm not sure everyone understands.

'My friends have become baby bores'
JOANNE GOOD, in her forties
a broadcaster on BBC Radio London, has decided not to have children

I do feel betrayed by other women of my generation. Many said they wouldn't have kids, then panicked. To actually choose to remain without children, like me, is still rare. Mothers don't envy us. They almost disbelieve that I've chosen not to have a child. Meanwhile they go on about the pain and sacrifice they've made as women – the sleepless nights, all of that. They know it's politically incorrect to exclude women without children, but it still happens. There's an arrogance in it.
Some of my friends are real baby bores. You can't talk to them because they're paying attention to the child. All they are is small versions of us, that's as interesting as it gets. But if you say anything, you're treated like the wicked witch of the west.

'I tell my younger employees not to end up like me'
KAREN BROOKS, 43
director of Aqua PR, is trying for a baby with her partner

The press treats women without children as selfish, which is unfair. You might not have wanted to be a high-flying superwoman, maybe you just didn't meet the right man?
When I was younger, I didn't worry about having children, but nor did I decide to focus on my career to the exclusion of everything else. Now, I'm struggling to have a child. I thought IVF was the last chance saloon, but I've found out that over the age of 42 they don't like to give you it. It was a real shock. People forget that women in their early forties are the first of a new generation – we were given the opportunity to see life, and were told modern medicine meant we could have children later, but it's turned out not to be the case. Women's lives have changed dramatically, but our fertility window remains the same. I've got some younger girls who work for me, and I say to them, 'Don't end up like this. It's a lot harder than you think.'

This is an extract from a feature taken from Psychologies. For further details and to subscribe, visit Psychologies. The current issue of Psychologies magazine is now on sale in newsagents nationwide