A former babysitter who was abused by ex-Team USA gymnastics sports doctor Larry Nassar has told him in court: "You are a repulsive liar."

Kyle Stephens was the first of nearly 100 women to testify against the 54-year-old this week as he is sentenced.

People in court wept as she told how Nassar convinced her own parents she was lying about the abuse.

Four-time Olympic champion Simone Biles on Monday said she was also sexually abused by Nassar.

At Tuesday's hearing in Lansing, Michigan, former family friend Ms Stephens told Nassar: "You convinced my parents that I was a liar.

"You used my body for six years for your own sexual gratification. That is unforgivable."

Ms Stephens told the court: "I felt I was losing my grip on reality, I started to question whether the abuse ever really happened.

"For my own sanity I forced myself to walk through the abuse step by step so I didn't forget that I was not a liar."

Ms Stephens told how Nassar repeatedly abused her from age six until age 12 during family visits to his home in Holt, near Lansing.

She told the court she continued to babysit for the family because she felt protective of the predator's young children and because she needed to pay for her counselling sessions to deal with the abuse.

"Complex feelings of shame, disgust and self-hatred brought me bouts of depression, anxiety, eating disorders and other compulsive conditions," Ms Stephens said.

"Perhaps you have figured out by now, that little girls don't stay little forever. They grow into strong women that return to destroy your world."

Judge Rosemarie Aquilina is expected to hand down a sentence on Friday.

Nassar pleaded guilty last November to molesting females at his home, at a gymnastics club and in his Michigan State University office.

He has been accused of molesting about 100 girls while he was a physician for USA Gymnastics, which trains Olympians.

Prosecutors are seeking at least 40 years in prison.

He has already been sentenced to 60 years in federal prison for child pornography crimes.

Donna Markham told the court on Tuesday how her daughter Chelsey committed suicide in 2009, years after Nassar sexually abused her during a medical examination.

"It all started with him," she said, describing her daughter's downward spiral into drugs.

Jessica Thomashow, 17, told the court how Nassar abused her between the ages of nine and 14 years old.

She told how he molested her in 2012 when she was 12 years old after she went to be treated for a stress fracture on her ankle.

Ms Thomashow said Nassar had preyed on her after telling her father that he could wait outside in the waiting room.

"Now I get flashbacks when I see male hands and it makes me feel scared and threatened," she said.

Ms Thomashow told Nassar: "What you did to me was so twisted. You manipulated me and my entire family. How dare you."

As she finished speaking, Judge Aquilina praised her bravery.

"You talk about being broken. Well, he's going to break while you're healing," she said just steps away from where Nassar sat with his head in his hands.

"More broken than he was as he committed these crimes against all of you," the judge continued, "because only a broken person would do such a vile thing."