Cynthia Daily, 48, told The New York Times in an article Tuesday she began a quest for her son's half-siblings by searching a Web-based registry for other children fathered by the same sperm donor.
Daily said she set up an online group to track the children and today they number 150 -- with more on the way.
Her story has prompted concern among parents, donors and medical experts about the potential negative consequences of having so many children fathered by the same donor.
Britain, France and Sweden limit how many children a sperm donor can father but there is no limit in the United States, only guidelines.
Law Professor Naomi R. Kahn of George Washington University said without limits the same donor could theoretically produces hundreds of related children.
It's that accidental incest could occur, Kahn said.