Gov. Dave Heineman of Nebraska signed a law on Tuesday banning most abortions 20 weeks after conception or later on the theory that a fetus, by that stage in pregnancy, has the capacity to feel pain. The law, which appears nearly certain to set off legal and scientific debates, is the first in the nation to restrict abortions on the basis of fetal pain.
The question of fetal pain, experts said, is one of intense, unresolved debate among researchers and among advocates on both sides of the abortion question.
Mary Spaulding Balch, director of state legislation at National Right to Life, said that scientific evidence related to the capacity for pain had not been heard by the Supreme Court, and that it opened a new legal question.
“You need five votes,” Ms. Balch said. “I think there are five on the current Supreme Court who would give serious consideration to Nebraska’s claim.”