A fertility doctor in Indiana is accused of being the father of at least eight people after admitting he used his own sperm nearly 50 times for patients who turned to his clinic when trying to conceive, according to a new report. The retired 77-year-old in the town of Zionsville could have even more biological children.

Dr. Donald Cline is facing two obstruction of justice charges for lying to authorities about using his own sperm at Reproductive Endocrinology Associates in Indianapolis instead of donated sperm. An investigation was sparked by complaints from two of his biological children against him. Cline on Monday pleaded not guilty to the charges, according to court records. Indiana news station WXIN-TV was first to report on the complaints in May from Cline's alleged children.

Suspicion that Cline was the father of multiple kids by patients at his fertility office came after one of the adult children took a saliva-based DNA test and discovered she was related to at least eight other people in the private personal genomics company’s database. Two more alleged children, whose mothers’ were patients of Cline’s, also had DNA test done and found they were related to 70 of Cline’s family members.

According to an affidavit, Cline told six people – all adults who claimed to be his biological children – that he donated his sperm around 50 times since the 1970s, although he told patients during time of insemination that they were receiving donations from medical or dental residents or students. He also told them that a male’s sperm would not be used more than three times.

After receiving complaints, which also came along with a Change.org petition written by one of the alleged children, the state initiated an investigation, during which Cline initially denied ever using his own sperm for patients. However, the affidavit said that paternity tests conducted in August proved Cline had a 99.9 percent probability of being the father of the two women who initially filed the complaint.

Cline retired from medical practice in 2009.

Although Cline’s personal donations may be considered unethical by many, it’s a practice that wasn’t all that uncommon for fertility clinics before the 1990s.

Director and co-founder of Colorado-based Donor Sibling Registry, Wendy Kramer, told the IndyStar she always advises people conceived through the help of a sperm bank before 1990 to check their mother’s fertility doctor first when searching for their biological father. The website helps connects parents, donors and offspring, and according to Kramer, checking a mother's fertility doctor is a crucial first step in determining the biological father for most children born before 1990.