NEW YORK — Laura Bennett isn't bound by convention. Professionally, at age 42, she's pursuing a midcareer switch into big-time fashion design. At home, she's a mother of five — with No. 6 due next month.

"It was nothing that we planned ahead of time," Bennett says. "It's more that we were enjoying all the kids.

"We have a happy home. Why not have as many children as we can?"

It's barely a blip on the nation's demographic radar — 11 percent of U.S. births in 2004 were to women who already had three children, up from 10 percent in 1995. But there seems to be a growing openness to having more than two children, in some case more than four.

The reasons are diverse — from religious to, as Bennett reasons, "Why not?"

The families involved cut across economic lines, though a sizable part of the increase is attributed to a baby boom in affluent suburbs, with more upper-middle-class couples deciding that a three- or four-child household can be both affordable and fun.

The Bennetts still stand out. Among other well-off families in Manhattan, three children is generally the maximum — one or two is much more common as parents contemplate private-school tuition of $25,000 a year even for kindergarten, and a real estate market that is far from family-friendly.

Bennett's husband, Peter Shelton, is a successful architect, and the family can afford child-care help while Bennett — also an architect by training — pursues her fashion-design aspirations as a finalist on the TV reality show "Project Runway." But their motives sound similar to those of other, less wealthy parents nationwide who have opted for five or more children.

Dr. Jeff Brown, a pediatrician affiliated with Greenwich Hospital in Connecticut's wealthy southwestern suburbs, has noticed a clear trend in recent years.

"I don't hear people say, 'We'll have two and then we're done,' where I used to hear that before," he said. "People are much more open to three-children families than they were 10 years ago."

However, really big families remain rare, Brown said, in part because many women are giving birth at older ages — they may not have their third child until in their 40s, when the prospect of a fourth might seem too daunting.

The Census Bureau says it has no national data specifying which demographic sectors are having more kids these days. But a leading expert on family size, Duke University sociologist Philip Morgan, says it makes sense that some well-off couples are opting for more children as concern about global overcrowding eases because of lowering birth rates overall.

"The population explosion — fears about that are over," he said. "People used to think that having more than two kids was not only expensive but immoral. Now, people say if you can afford three kids, four kids, that's great."