An Indianapolis fertility doctor accused of impregnating dozens of women using his own sperm without their knowledge has said he will plead guilty to obstruction of justice charges.

Attorneys for physician Donald Cline said he is planning to admit that he fathered more than 20 children by inseminating women with his own sperm at his clinic in northwest Indianapolis in the late 70s and early 80s.

Cline was charged with two counts of obstruction of justice in September 2016 after Marion County Prosecutor's Office became aware of eight people who were found to be genetic siblings after they used a series of DNA analysis companies and ancestor websites to trace their background.

In each case, the children – now all adults – said their mothers became pregnant after using Cline's clinic. Court documents show paternity tests prove there is a 99% likelihood Cline is the biological father of at least two of his patients' children, according to Indy Star.

However, when some of the siblings arranged to meet up with Cline in 2016, he told them he donated his own sperm "around 50 times" during the course of his career to help women get pregnant.

After an investigation was launched, Cline told authorities he never used a donor's sample for more than three successful pregnancies and eventually switched to using frozen sperm from Follas Laboratories in Indianapolis. He also told the Attorney General's Office that he never used his own sperm.

It was on the basis of these statements that Cline was subsequently charged with obstruction of justice. He has indicated he will officially plead guilty to the charges at his next court appearance on 14 December. It is not clear whether Cline will admit to one or both charges against him.

Matt White, who is one of those fathered by Cline, told WXIN: "This wasn't just a handful of kids or mothers that this happened to that resulted into a handful of children.

"We're now into several dozen. And it's going to continue to grow."

Amber Stafford, another one of Cline's biological children, added: "It was a kind of reassurance that even though he wasn't here and didn't say, 'I'm guilty,' it kind of gives you that feeling that he is owing up to what he did and admitting that what he did was wrong."

It is unlikely Cline will face jail as there are no laws in Indiana which prevents fertility doctors using their own sperm to treat patients, but he may be stripped of his medical licence.