"In short it's because there is so much more opportunity for women these days," she said in an e-mail exchange. "You don't need kids to fill your life."

Like Roggenkamp, Defago observed that not having to raise children had given her and her husband a great many material advantages.

"We have a wonderful life," she said. "We have a home in London and a home in Spain. We work hard over the summer and take the winter off to travel. We are not tied into school timetables."

Nonetheless she said that in researching her book she found that financial considerations were not determining factors for most people who decided that children were not an option for them.

Carole Matthews is a novelist and child-free as well, in her case because of illness.

"It was when I was researching my latest novel, 'With or Without You,' that it really brought it home to me that kids in the Western world really have become a lifestyle choice," she said in an e-mail exchange.

"Go out to any country in the developing world and children are still very much an integral part of society — not just a desirable 'bolt-on,' " she said. "They need children to work the fields, look after siblings and to provide for the parents in their old age — they simply can't manage without them on a very basic level. It isn't a choice whether you have kids or not."

One common misperception is that being child free is about disliking kids and their parents, according to Rachel Pildis, 39, of Oak Park, Ill.

Pildis has been a member of the Chicago chapter of the international child-free network called No Kidding! since 1999. She says plenty of people without kids enjoy being around children. They're just happy to send the kids home with their parents at the end of the day, she said.

Pildis joined No Kidding! — with about 200 members in the area who enjoy activities such as book clubs, hikes and dinners — because she and her husband wanted to meet other child-free people who shared their lifestyle.

Roggenkamp, who has decided not to have kids, and her husband are young — he is 27 — and so have not totally ruled out a change of heart, but think that is unlikely.

"My husband and I have talked about the very slight chance of changing our minds and we have decided either he will have a vasectomy, or I will have a tubal ligation by 2008," she said.

"In the meantime, I take birth control pills religiously. If I were to get pregnant, I would have an abortion.

"The chance of us changing our minds is infinitesimal. Neither of us has ever had a desire to take care of children and I don't suspect that will happen in the future."