Yiskah Rosenfeld never had baby fever. She didn’t long for a child or hear her biological clock ticking in the giggles of other women’s newborns.

Yet, by 42, Rosenfeld, single with a full and happy life, decided it was time. If she didn’t at least try to conceive, she’d regret it for years to come.

“I realized that for me part of what it is to be human is to be a parent,” says Rosenfeld, an Albany, N.Y., poet and educator who is pregnant from artificial insemination through an anonymous donor. She is due this month. “I bought into the myth that you only have a child if you have a partner. It took a while to overcome that fantasy.”

Rosenfeld accepted that Mr. Right may not show up in time. And since adoption can be a long, challenging process with no guarantees, particularly for single parents, it is estimated that 50,000 women a year start families on their own, according to Mikki Morrissette, founder of the Minnesota-based online forum Choice Moms. It is an estimate, because the fertility industry is not required to report on these statistics.

Many single women use known or anonymous donors through sperm banks such as California Cryobank in Los Angeles, the nation’s largest. Scott Brown, the bank’s director of communications, estimates that within 20 years, single heterosexual women will represent more than half of its clientele. Brown says about 10,000-12,000 single women a year visit a sperm bank. Those numbers are reflected in two films this year, last April’s “The Back-up Plan” and “The Switch,” which opened Friday.

The trend has roots in the 1970s feminist movement, which opened doors to better, higher paying jobs for women and the means to support a family, says Jane Mattes, a New York psychotherapist who founded the support group Single Mothers by Choice in 1981. It is the first and oldest organization of its kind.

“Besides the economic aspect, it was also the message that women were competent individuals and could support a family,” says Mattes, a single mom who had her son in 1980.

Sperm banks proliferated in part as an outgrowth of the feminist movement, Mattes explains, and by the early 1980s, many were open for business. Those like Berkeley’s Sperm Bank of California, which originated in Oakland, made it their mission to provide services to women who could not receive them elsewhere because of discrimination based on marital status or sexual orientation, says Executive Director Alice Ruby.

Before that, doctors would perform artificial inseminations on single women in secret.

“The biggest challenge was not in finding sperm but that physicians were somewhat slow on being willing to inseminate single women and lesbian couples,” Brown says. “That remains an issue today. I get calls from women in certain parts of the country, like the South, who cannot find physicians willing to help.”

Whether they use sperm donors or become pregnant by chance, these single mothers still face raised eyebrows and other obstacles, including infertility and lack of resources in a prenatal health care system geared toward couples. Even arriving at this decision — grieving “happily ever after” — can be a long, emotional journey, says Collin B. Smikle, medical director of Laurel Fertility Care in San Francisco.

“The first fallacy is that they have control in this matter,” Smikle says. “Typically these are career track women who postponed marriage and pregnancy hoping that Mr. Right will show up, and he doesn’t. Because they were successful in building a career, it’s hard for them to accept that no matter what they do, the biological clock doesn’t stop.”

Fertility declines with age, but not all women older than 40 have trouble conceiving. Rosenfeld got pregnant with ease at 43. Another myth is that all “choice moms” are older than 35. But, there are women as young as 25 who “already know this is what they want,” Morrissette says.

“This generation has had a lot of independence, and having a lifetime partner is not necessarily a must for them,” says Morrissette, author of “Choosing Single Motherhood: The Thinking Woman’s Guide” (Be-Mondo; 2006). “Perhaps they’ve come up through a single parent household. Or they don’t want to compromise when choosing a partner.”