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More women in the developed world are choosing not to have children. So why do friends, family, colleagues and even strangers think it's OK to question their decision?

We've come a long way, baby. Until a few decades ago, it was widely assumed that a woman would marry and, soon after, the stork would arrive with a special delivery.

Today, there are many more choices - or more openness. To have a baby out of wedlock. To have a baby without a father. To have a baby and return to work. To have a baby and give up work. To have fertility treatment, and then a baby (or not).

Find out more Woman's Hour on Radio 4 had a child-free by choice special on Wednesday 28 July

And a phone-in on Thursday 29 July Catch up with the iPlayer

But what about not becoming a mother at all? Studies in the UK, Europe and the United States show this is now the choice of significant numbers of women.

Once this was considered insane or unnatural. Even today, it is viewed with suspicion - women with no desire to procreate say they sometimes face awkward questions and disapproval.

"A woman at work was recently quite shocked by my saying I didn't want children. She said: 'You're a woman, you were born with a womb, God gave a womb so we could procreate'," Jenny, aged 25, told BBC Radio 4's Woman's Hour.

"My friends and I have occasionally likened coming out as child-free to coming out as a gay person 40 or 50 years ago. There's the same sense of shock - perhaps that's too strong a word. But it's a lifestyle people don't expect and it may challenge their world view," says 31-year-old Rhona Sweeting.

Sociologist Dr Catherine Hakim, of the London School of Economics, has studied voluntary childlessness in the UK and Europe for many years. She says this is a new social phenomenon, with women now open and positive about such a lifestyle choice.

"An early study in Canada years ago found roughly half of all the women who were childless in their 40s actually chose to be that way from a very early age.

"But very many of them didn't say so because of the social pressure they would get if they mentioned a preference for staying childless.

Maybe not baby One in five UK women will not have children, many by choice

Among female graduates, this rises to one in three according to some studies

Teenage single mums are becoming biggest social group giving birth in the UK

Infertility affects 2-3% of women globally, says the UN

US Census Bureau says 36% of American women have no children Advice on step-family life from BBC Health

"The contraceptive revolution has completely changed perspectives. Whereas before having children just inevitably happened to all people who got married or had sex, now it's something you have to make a choice about."

And the disapproval some experience? "It's a question of generations and age. There was a stigma in the past."

But suspicion of childless women hasn't entirely disappeared.

Julia Wallace, at 40 a step-mother to three children who live elsewhere, says she is questioned about why she has no baby of her own.

"They say, 'you don't know what you're missing, you won't know until you've had a child that that's what you wanted to do'. That's a hypothetical question - if you've got no motivation to have a child in the first place, why would you do it? I wouldn't chose to become a nurse on the chance I might love the career once I get there."

Image copyright Other Image caption Forgotten something? Actually, no

Natalie Haynes, 35, has been with her partner for four years and has never dreamed of the pitter-patter of little feet. "My parents are very well trained [not to ask]. I worked hard at school and at college, then I ran away and became a comedian - that worked out, so they've already won the lottery. I think my mum might like grandchildren, but I have a brother and it's his problem."

But not everyone is as breezy about their decision as Natalie.

Beth Follini counsels women agonising over whether to reproduce. It's a decision she herself has struggled with. Until her early 30s, she hadn't wanted children and told her partner so. "Then I just started to feel this urge. I spent a year or two battling it out and in the end I decided I wanted a child. But I know that if I hadn't, I would have a very different but equally fulfilled life."

Many of her clients do not want children but feel pressurised. "Often this pressure comes from friends who have had children - 'you don't know what you're missing' or 'you'd make a great mum'. Or joking that you hate children. Sometimes it's from parents hoping for a grandchild."

But it can be the most passing of acquaintances who pass comment.

"Many people assume if you a single and child-free that you haven't met the right man yet. But if you are in a relationship, they ask 'when are you taking the next step?' A woman's fertility status is still very much considered public property. There are still assumptions about women's role in society, about families and about family size."

Image copyright Other Image caption To work or not? Mothers also find everyone has an opinion on their choices

Lisa Davies, 38, says the assumption is often that she cannot have a baby. "What I'm unhappy about is people looking at me and speaking to me - very often unashamedly - as if there is something wrong with me. As with other choices that you make, the key is it's not for everyone."

In the United States, New Yorker Melanie Notkin, founder of the Savvy Auntie website, wants a national day to celebrate child-free women who are loving aunts or godmothers.

"It would be a chance for these women to feel whole, for everything that they are, instead of having to focus on all the things they're not - ie mothers."

She says modern families need extra hands. "Mothers and fathers are working overtime. So an aunt who is able to give quality time to the family, especially to the children, is very welcome."

Research by Paola Buonadonna and Vibeke Venema, compiled by Megan Lane.