Teresa Heinz Kerry (search) nearly underwent an abortion (search) some 30 years ago on a doctor's recommendation because she had been taking cortisone early in her pregnancy, but a miscarriage rendered the decision moot.

In an interview that will air Friday on ABC's "20/20," the wife of Democratic presidential candidate John Kerry (search) discussed her experience, the clamor for her to release her income tax returns, the campaign and her reputation for outspokenness.

During her first marriage, Heinz Kerry said she wanted a fourth child after the birth of her son Christopher in March 1973. She said she had a "severe reaction to something," was taking heavy cortisone (search) medicine and did not realize she was pregnant.

"I told my doctor I think I'm pregnant and ... he said well then if you're pregnant, you have to abort that baby ... and I was very upset ... I didn't want to have an abortion, but they gave me 15 days because it was early and the night before I was due to go in, I miscarried it. So God was very kind," she said.

Heinz Kerry stressed that she favors abortion rights "because I'd like to have that choice myself."

Speaking to interviewer Barbara Walters, Heinz Kerry said, "I presume that most women will look at a choice like that as a terrible choice. But they should be given the chance to make it as I was."

Heinz Kerry and her late husband, Sen. John Heinz of Pennsylvania, have three sons. John Kerry has two daughters from a previous marriage.

Heinz Kerry described herself as "pro-choice" — a political stance that has caused problems for John Kerry in recent weeks, as some church leaders have said Roman Catholic politicians should not receive communion (search). Kerry, a Massachusetts senator, has been attending church regularly and has not been denied communion.

In the interview, Heinz Kerry, 65, also said she won't release her personal income tax records because she doesn't have the right to share her sons' records with the public. Some of their records are commingled with hers, she said, adding that she is working on separating the records so she can release her own tax information.

Heinz Kerry also said she would have been terrified if her husband had told her when they got married that he wanted to run for president. If she had told him she was against it, Heinz Kerry said she doesn't think Kerry would have run.

"I think he believes, and I do too, this is such arduous work that it needs the commitment, intellectual if possible, certainly emotional, to ride this," she said.