A fertility doctor in Indiana in the United States has been accused of being the father to eight of his patients children… but that number could very well rise.

Dr Donald Cline, 77, has admitted to using his own sperm nearly 50 times for his patients who were trying to conceive throughout his career.

According to a new report, Dr Cline is facing two obstruction charges for lying to the authorities about using his own sperm instead of using the donations provided at the Reproductive Endocrinology Associates (REA) company in Indianapolis.

The investigation began when one of Donald's biological children took a saliva-based DNA test and found out that he was related to eight other people on the REA's database.

Two more of the doctor's alleged children followed suit and took a DNA test to find out they were all related.

According to an affidavit, Donald told the patients that sperm would not be used more than three times, but since the 1970s, he has used his own around 50 times. He also promised his patients at the time that all the sperm was donated by medical or dental residents or students.

After one of the eight alleged children created a petition on Change.org, the state started their investigation, during which Mr Cline denied ever using his own sperm.

However, the affidavit states that the paternity tests carried out last August showed Donald had a 99.9 percent probability of being the father of the woman who carried out the petition.

Dr Donald Cline retired from practice in 2009 and the investigation is still ongoing. More children are now being tested to find out if he is their father.