Sarah Palin discussed abstinence and teen pregnancy in the interview with Van Susteren.
"You get behind that, that ideal of, yes, abstinence, you know?" the new grandmother, 44, said. "Hey, don't get pregnant. Well, get beyond that when it happens, and then you deal with it. Life happens. Life happens and you deal with it, and Bristol's dealing with it wonderfully.
"Not the most ideal situation," she added. "Certainly you make the most of it."
Last October, Johnston told the Associated Press he had been dating Bristol Palin since freshman year of high school and the couple had long planned to get married.
"We were planning on getting married a long time ago, with or without the kid," Johnston told the AP. "That was the plan from the start."
He went on to describe rough wedding plans, even naming two friends he had asked to be groomsmen.
"We both love each other. We both want to marry each other. And that's what we are going to do," Johnston said at the time.
Four months later, in the interview with Van Susteren, new mother Bristol Palin sounded more tentative about the couple's wedding plans. But she said Johnston saw the baby every day and described him as a "hands-on" dad.
News that the couple had ended their relationship first emerged last week.
Johnston told the AP on March 11 that he and Palin had decided "a while ago" to end their relationship.
The Associated Press contributed to this report.