Their Mothers Chose Donor Sperm. The Doctors Used Their Own.

The DNA test matched her to relatives of the doctor himself. “Once I had the matches, I realized it was the doctor, and I was like, yuck, gross,” she said. “When I talked to my mom about it, she felt violated.”

“Until now, I’ve been able to handle what life has thrown at me,” she added. “But this was this weird identity crisis.”

Reached by phone by a reporter at his home in Little Rock, Ark., with questions about Ms. Tucker’s conception, the retired physician, Dr. Gary Don Davis, said: “Well, that’s surprising. Let me check on that. Goodbye.”

Further attempts to reach him were unsuccessful, and he died in June.

Why would doctors secretly substitute their sperm for that of a donor, or even a husband?

Dr. Madeira, the law professor who has been tracking many of these cases, said that some specialists may simply have thought it was smart business. Frozen sperm was not the recommended medical standard until the late 1980s, and many physicians may not have had ready access to sperm when patients sought help.

“They could have self-justified their malfeasance in an era of ‘doctor knows best,’” Dr. Madeira said. “In their minds, they may just have been helping their patients by increasing their chances of getting pregnant with fresh sperm for higher fertilization rates.”

But others, she speculated, may have had darker motivations. “I would bet a lot of these doctors had power reasons for doing this — mental health issues, narcissistic issues — or maybe they were attracted to certain women,” she said.