Now, the first of those meetings is about to happen.
A San Francisco Bay-area woman who turned 18 on Tuesday plans to contact her biological father sometime in the next few months to thank the stranger and to learn more about their shared genetic history.
Claire, who asked that her last name and hometown be withheld for now, hopes to answer questions she has had her whole life. Among them: Why is she taller than most of her mother's family? Why is her sense of humor so different from her mother's?
"I really have a bond to him. I have always felt that," Claire said this week. "I cannot recall a time when I didn't think about it."
The meeting will take place after the sperm bank determines how the man - who still lives in California and has known this day might come - wants to be contacted.
It will be a big moment for the field of artificial insemination, which is slowly becoming more open after being shrouded in secrets and lies for more than a century.
"It just all seems to be happening in a timely manner, parallel with the open adoption movement, people wanting to know their identity," said Maura Riordan, the Sperm Bank of California's executive director.
Estimates of the number of American children born each year through artificial insemination range from 30,000 to 75,000.
Before the advent in the 1970s of sperm banks that maintain a collection of frozen donations, the sperm used for artificial insemination was often provided on the spot by medical students or doctors, and was given only to married couples in which the men were sterile. The couples generally were advised to keep it a secret, leading to some awkward and painful experiences.
"I suspected my father wasn't my father - we suspect early on," said Bill Cordray, a 56-year-old architect in Salt Lake City who learned when he was 37 that he was conceived through artificial insemination. "I worried my mom had had an affair."
Cordray has determined that the sperm donor is almost certainly one of 30 medical students who graduated from the University of Utah in 1945. He has been building up the courage for years to write letters to them.
The nonprofit Sperm Bank of California sought to demystify the process - and expand it to serve single women and lesbian couples - when it was founded in 1982 by the Oakland Feminist Women's Health Center.
From the beginning, the sperm bank asked donors if their offspring could someday contact them. Men who say no can still donate. Those who say yes cannot reverse the decision later. Eighty percent of the bank's clients now request a donor willing to release his identity.
In that first year, several men agreed; about 10 of their offspring are turning 18 this year.
"I always thought if I was looking at the world through the eyes of woman, I would want to know where the genetic material came from," said technology consultant Mike Smith, 49, a married father of two who has been told that a child conceived with his donated sperm will contact him after turning 18 in May. "I was surprised that secrecy was the norm."
Since 1983, a few other sperm banks have also begun releasing donor identities. Some banks provide photographs of their donors; others offer to ask the men years after their donation whether an offspring can reach out to them.
In some countries, such as Sweden, donors are now required to release their identities.
As more children reach out to their mothers' sperm donors, it raises legal questions such as whether they can seek inheritance and child support. But laws in most states would prohibit such moves, said David Towles, spokesman for Xytex Corp., a Georgia-based sperm bank with some open-identity donors.
Claire's mother, Irene, who was single and 40 when she sought out the Sperm Bank of California, has since married. She supports her daughter's plans. Claire's mother was honest with her about how she was conceived, and the young woman was similarly open about it with her friends.
Claire calls the man "my dad" (sperm banks prefer "donor" or other clinical terms) but said she is not looking for a father figure. She does hope he becomes a friend, perhaps someone to exchange Christmas cards with.
Claire, an only child, knows the donor also provided offspring to other families, meaning she has half-siblings somewhere out there.
"It's kind of scary," she said with a laugh, "to think how small my family is now and how potentially large it could be."
By Brian Bergstein © MMII The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed