When Diane Carr turned 37 with a compelling desire to have a baby and no true love to have one with, she began, gingerly, to explore the other option she had filed in the back of her mind.

Like other single women who have found themselves sifting through online profiles of anonymous sperm donors recently, Carr, a real estate broker in Atlanta, was quickly convinced that buying sperm was the easiest way to have a baby without a partner. She also concluded that it has quietly become a socially acceptable choice, if only because so many are making it.

Carr's hairdresser, it turned out, knew someone who had just conceived that way, as did one of her own clients. An Atlanta chapter of a national support group for "single mothers by choice" formed two years ago and had 26 members.

On the Internet, Carr discovered hundreds of pregnant single women trading notes. Some were arranging to send one another their leftover sperm.

"Five years ago you never heard about this," said Carr, who had the insemination procedure performed this fall. "Now you can talk about it, and it's OK."

In her effort to become a lone parent, Carr has plenty of company. The support group she joined is 25 years old, but it has grown from 12 to 24 chapters across the country in the last three years. About three-quarters of its 4,000 members used sperm donors. Sperm banks, which once catered largely to infertile and lesbian couples, are seeing a surge in business from single women, as are obstetricians who perform artificial inseminations.

The groundswell of single women deliberately having babies reflects their increased ability to support a family. It helps, too, that the Internet has done away with the need to leave the house to find a donor. A woman can now select the father of her child from her living room and have his sperm sent directly to her doctor. It is faster and cheaper than adoption, and it allows women to bear their own genetic offspring.

Single women have always found adoption rules more restrictive than they are even for gay couples. Many hesitate to simply have a sexual fling or use a "known donor" for fear that the father may someday stake a claim to the child. But thousands are gravitating to sperm bank Web sites, where donor profiles can be sorted by medical history, ethnic background and a wide range of physical characteristics. Like an online dating service where no one ever dates, the sites feature written answers to questions such as "What is the funniest thing that ever happened to you?" Some women screen for men with no cancer in their family. Some search for a man who might have been their soul mate. Others are more pragmatic.

"You're paying for it, so you kind of want the best of the best," said Anna Aiello, 38, of Moriches, N.Y., on Long Island, the mother of 1-year-old twins, who saw her ability to select a 6-foot-2-inch blond, blue-eyed, genetic-disease-free donor as some consolation for not getting to fall in love with someone who would most likely have been more flawed.

What it costs

Prices at sperm banks range from about $150 to $600 per vial, plus shipping. At some banks customers can pay extra for a donor's childhood photograph or a tape recording of his voice. Fairfax Cryobank, one of the largest, charges more for donors who have doctorates.

Veteran "choice moms" say more single women are trying to conceive in their mid-30s rather than waiting. Because they are starting before their fertility declines, they are having more success. Some are even having second children.

"It's not necessarily Plan B anymore, it's just the plan," said Melissa Singer, 46, a member of Single Mothers by Choice, a national support group, who had a donor-inseminated daughter 10 years ago. "It means there's a lot less desperation as a whole in the group."

No one tracks the number of women who actively choose single motherhood, but their ranks, while still small, seem to be increasing quickly. According to 2004 census data, about 150,000 women with college degrees have children under 18, have never been married and are the only adult in their household, triple the number recorded in 1990. Family sociologists say women in that group are likely to be single by choice, not chance.

"Women who order sperm are engaged in a kind of agency that is new and is gaining momentum," said Rosanna Hertz, a sociologist at Wellesley College who is working on a book called "When Baby Makes Two." "It's different from women who adopt, who are not breaking sexual norms."

Regrets haunt some

Historically, far fewer women with high incomes and college educations have had children out of wedlock than those with less money and schooling. But some high-achieving women may be shifting their behavior based on the lessons of a generation that precedes them.

Professional women in their 50s regret not having had a child far more than not having gotten married, said Sylvia Ann Hewlett, an economist whose 2002 book "Creating a Life: Professional Women and the Quest for Children" found that more than a third of women with high-status jobs were childless at 40.

"When push came to shove, the child was more important than the partner," Hewlett said of the women she interviewed. "It was an ever-present source of regret, where they were not so actively mourning the absence of a husband."

The boom in high-tech fertility treatments for women over 35 has raised women's awareness of the limitations both of their bodies and their demographic. But some women in their 30s who have seen friends divorced or in unhappy marriages say they are not willing to settle for "Mr. Almost Right" to have a baby.

Making decisions alone

Many single women still find the choice to get pregnant met with incomprehension or even hostility from friends, family and some strangers. The most common accusation is that they are selfish, because of the widely held belief that two-parent homes are best for children.

Mothers who choose their solo status say the problems that have traditionally burdened families headed by a single mother -- poverty, abandonment by fathers, teenage motherhood, parental conflict -- do not apply to them.

But some suspect that what makes people uneasy is not so much their status as single mothers but that they achieved it by short-circuiting the traditional act of procreation. Experts on nontraditional families say the use of anonymous donors without a more conventional reason, like infertility or homosexuality, may seem more threatening to men's role in the family.

Some single mothers do relish their autonomy, which they say can more than compensate for not having a partner to help change the diapers. Every decision, from what to name their children to how to discipline them, is theirs to make without negotiation.