A growing number of older men and women are welcoming newborns. But the real question is: What’s it like to be changing diapers at 50?

In the last few years, a slew of celebrities, including Diane Keaton, Joan Lunden, and Sharon Stone, have embraced motherhood in midlife. They are a high-profile reflection of what’s happening all over the country.

The birthrate for women 45 and over more than doubled between 1990 and 2002, according to a Centers for Disease Control and Prevention report, and adoption at midlife is on the rise too.

“Nobody keeps those numbers,” said Adam Pertman, author of “Adoption Nation,” and executive director of the Evan B. Donaldson Adoption Institute in New York City, “but there’s no question that the number of older adopters is growing.”

This Baby Boomer baby boom has even attracted publishers’ attention. A glossy new magazine called, Plum, just out from the American College of Obstetricians and Gynecologists, targets pregnant women over 35. Likewise, the magazine, Conceive, which deals with fertility issues, is finding a ready-made audience of baby-minded women chasing menopause.

While it’s easy to wonder about this new wave of midlife babies, the plain truth is that these older moms and dads are clearly delighted to devote what might have been their leisure-filled retirement years to the frenzy of childcare and all the responsibilities that go with it.

Producing an infant later in life isn’t easy, of course. No one throws out her birth control pills at 50 and nine months later delivers a baby. These children are hard won, through fertility and adoption processes that are time-consuming and expensive – sometimes as much as $500,000, or more.

Parenting is rarely easy. But parenting in midlife has special challenges. First there is the sheer exertion – getting up in the middle of the night for feedings and diaper changing, or keeping up with a curious toddler. Then again, older moms and dads believe they have more patience and understanding than they did when they were younger.

In addition to the challenges facing any parent raising a child today, being an older parent can mean being an outcast-even an object of derision. In the movie, Father of the Bride II, Steve Martin does a whole riff on the subject, telling his wife, played by Diane Keaton, “Between us, we’re almost 100 years old. Our kid will be spending his adolescence in a retirement home. At the movies, it’ll be one child, two seniors.”

When reality-show host Joan Lunden, 55, announced the impending birth of a second set of twins by a surrogate last winter, a Web site for moms prickled with jibes: “I’m younger, and I don’t want one set of twins, let alone two! Honestly! Is the woman nuts?” wrote one woman.

Such busybody comments are frequent enough that another site, www.mothersover40.com, has posted suggested responses. Comment: “I can’t believe you’re pregnant, and at your age.” Reply: “I can’t believe you’re so rude.” Comment: “Aren’t you too old to have another baby?” Reply: “Evidently not.”

At one point or another, many midlife parents will also encounter the classic experience of being mistaken as the grandparents. Some laugh it off. But Diane Aldrich bristled at more direct putdowns: “I couldn’t believe what people thought they could say to a pregnant older woman. They’d ask, ‘What were you thinking?'”

Claire Gruppo, another midlife mom, has a different theory about why older parents get so much grief, “It shakes up the social order of expectations. I remember 15 years ago, when the first single women were deciding to have kids on their own. People were horrified. We’ve pushed through all of that. This is the new frontier.”

Carolyn Pelcak points out that in a world where Clint Eastwood and Warren Beatty had kids when they were in their 60s, we reserve our harshest criticism for older moms, not dads. “For a man it’s a wonderful thing, very macho. But for women it’s still taboo. There should not be a stigma for a woman who wants to be an older mother.”

Even if these parents feel-and act-much younger than they are, there is no doubt that for some their age gives them pause when they look 15 or 20 years ahead.

Older parents often wonder whether they will be alive to see their children graduate from high school or college and get married, or wonder if their children may all too soon have to take care of their elderly parents.

Because of these concerns, most older parents try to take extra special care of themselves so as to increase the odds they’ll be around for many years to come.

Even assuming they remain in good physical health, midlife parents face another challenge, which is how to stay financially healthy as well. Many may find themselves working well beyond the traditional retirement age, just so they can send their kids to college. Being realistic, and planning in advance, can be a big help.

And, despite the challenges and difficulties, most midlife parents wouldn’t have it any other way because of the sheer joy a child can bring at any stage of life.