Gay and Lesbian Adoptive Parents: Resources for Professionals and Parents-Gay and Lesbian Adoptive Parents: Resources for Professionals and Parents. However, the statistic is referenced to a 1990 book that was published by the editors of Harvard Law Review (Editors of the Harvard Law Review. (1990). Sexual Orientation and the Law. Cambridge, MA: Harvard University Press.)) Upon further digging, the book arose from a lengthy piece published in the May 1989 issue of Harvard Law Review.
That article contains a sentence that reads, "Approximately three million gay men and lesbians in the United States are parents, and between eight and ten million children are raised in gay or lesbian households." That statistic is referenced to the American Bar Association's annual meeting held on August 25, 1987 at which there was a forum for "family law experts." No further details are provided. In short, the figure was likely an estimate from one of the participants at that forum.