"We wanted more children. All I'd ever wanted was a normal family, a couple of kids.
"But it was all falling apart and the baby would have been due around the time of his court case," she told the Sun.
"I knew I couldn't bring another baby into the world, everything was a mess. I never thought I could have an abortion. Neither of us wanted to but we agreed it was for the best.
"It was heartbreaking but I felt I had no choice."
The 31-year-old Johnson is due to be released from prison in South Yorkshire this month after being sentenced to six years behind bars three years ago.