A retired fertility doctor in Indianapolis is facing charges after lying to authorities about using his own sperm to inseminate patients without their knowledge, court documents allege.

Donald L Cline, 77, appeared at Marion Superior Court on Monday and is facing two felony counts of obstruction of justice after he allegedly told investigators that he never used his own sperm on patients, The Indianapolis Star reports.

According to the probable cause affidavit, Mr Cline told six adults that he had donated his own sperm nearly 50 times since the 1970s. Donations were made with live sperm in the 70s and 80s rather than frozen samples, making the case against Mr Cline somewhat unclear.

Sean Tipton, a spokesman for The American Society for Reproductive Medicine, told The New York Post that the association did not have any guidelines regarding doctors using their own sperm during the time period.

Mr Cline previously told his patients that the sperm was from medical residents or students, but they didn’t believe his story.

One of the adults who believe they are Mr Cline’s children took a saliva-based DNA test and found that she was related to at least eight other people in the private company's database. Two others learned their mothers were patients of Mr Cline and found that they were related to 70 of his relatives.

"I can emphatically say that at no time did I ever use my own sample for insemination," Mr Cline wrote in his legal response to the sibling’s complaints. He also accused them of slander and libel.