While the rapper, 32, has addressed the issue through her music previously, she has never openly talked about it.
She told Rolling Stone: "I thought I was going to die. I was a teenager. It was the hardest thing I've ever gone through.
"[It's] haunted me all of my life. It's be contradictory if I said I wasn't pro-choice.
"I wasn't ready. I didn't have anything to offer a child."
On track All Things Go, taken from her new album The Pink Print, Nicki reveals her child would have been 16 now, meaning she would have been 15 at the time.
She raps: "I want Caiah [Micaiah, Nicki's 16-year-old brother] to go to college just to say we did it.
"My child with Aaron would've been 16 any minute. So in many ways Caiah is both of them.
"It's like he's Cai's little angel looking over him."
Although she has never confirmed the age she was while pregnant, or who 'Aaron' is, it is thought Nicki may have had the abortion while studying at LaGuardia performing arts school in New York.