Most Americans remain opposed to overturning the controversial Supreme Court decision in Roe v. Wade, which 40 years ago legalized abortion at least in the first three months of pregnancy, according to a poll released Wednesday.

The poll by the Pew Research Center found that 63 percent of Americans believe that Roe v. Wade should not be completely overturned, compared to 29 percent who believe it should be. These opinions have changed little from surveys conducted in 2003 and 1992, Pew reported.

Michael Dimock, director of the Pew Research Center for the People and the Press, said it is uncommon to see so little change in attitudes on a controversial issue.

"They really haven't changed a lot over the years which is kind of interesting because a lot of other social issues have changed a lot, gay marriage being the most notable example," said Dimock.

He noted that opinions on issues such as gay marriage sometimes have a sharp generational divide, with younger people more likely to favor it, so national feelings change over time.

But the abortion issue shows only modest generational differences, and no gender gap.

Those most likely to favor upholding Roe v. Wade at 69 percent are the "baby boomers" aged 50-64, who were children or young adults when the case was decided on January 22, 1973. This group was followed by those 18-29 years old, who favored upholding the decision by 68 percent.