LOS ANGELES — When Tina Roggenkamp and her husband, Mark, decided to keep their marriage free of children, they took a lot of things into account.

They considered their mutual desire for greater freedom, something that enabled her to get a graduate degree and start a small consulting business. There was also their enjoyment of what she called "smaller things" like being able to sleep late when they wanted and dine out whenever the mood struck them.

But there were larger issues as well.

"We worry about global warming," said the 25-year-old who lives in Charlotte, N.C. "We worry about what the world will be like in the future. There's so much uncertainty, and I can't see bringing a life into such a world."

Growing number of couples around the country are electing to have what they call "child-free" relationships.

The latest Census Bureau figures show about 18 percent of women between the ages of 40 and 44 say they have never conceived a child. The percentage has grown steadily since 1976, when 10 percent of U.S. women reported never conceiving a child.

Some childless couples report that not everyone is comfortable with this trend. Jennifer Shawne, 32, author of "Baby Not on Board: A Celebration of Life Without Kids," said she has even been accused of being un-American for not opting for motherhood.

"There is this assumption that all women have a biological clock that one day is going to start ringing, and we're going to become baby maniacs who have to give birth no matter what," Shawne added. "But that's just not true."

A lot of young women today, Shawne said, are realizing that the feminist ideal that you can have it all — kids and a successful career — is not feasible.

There are many reasons why a woman might not conceive, but the conscious decision to avoid children appears to be playing a larger role these days.

Many groups have formed that seek to connect these couples around the country.

No Kidding! and The Childfree Ring are among the most active. Some offer bumper stickers. One reads: "If I want to hear the pitter-patter of little feet, I'll put shoes on my cat."

Emily Connolly and her husband hadn't even cut the cake at their wedding reception before friends and family started asking: When are the babies coming?

"Um, they're not," Connolly wanted to say.

Instead she deflected the questions and wondered for about the millionth time why many people assume that all couples want kids.

Connolly, a 24-year-old Chicago retail saleswoman, and her husband, Jimmy, have no plans to have children.