""In Roe v. Wade, 410 U. S. 113, the Court held that a woman's right to decide whether to abort a pregnancy is entitled to constitutional protection. That decision . . . is now part of our law. . . ." Planned Parenthood of Central Missouri v. Danforth, 428 U. S. 52, 428 U. S. 101 (STEVENS, J., concurring in part and dissenting in part)."