"Three cases in the sensitive and earnestly contested abortion area provide essential background for the present controversy. In Roe v. Wade, 410 U. S. 113 (1973), this Court concluded that there is a right of privacy, implicit in the liberty secured by the Fourteenth Amendment, that "is broad enough to encompass a woman's decision whether or not to terminate her pregnancy." Id. at 410 U. S. 153. This right, we said, although fundamental, is not absolute or unqualified, and must be considered against important state interests in the health of the pregnant woman and in the potential life of the fetus. "These interests are separate and distinct. Each grows in substantiality as the woman approaches term and, at a point during pregnancy, each becomes 'compelling.'" Id. at 410 U. S. 162-163. For both logical and biological reasons, we indicated that the State's interest in the potential life of the fetus reaches the compelling point at the stage of viability. Hence, prior to viability, the State may not seek to further this interest by directly restricting a woman's decision whether or not to terminate her pregnancy. [Footnote 7] But after viability, the State, if it chooses, may regulate or even prohibit abortion except where necessary, in appropriate medical judgment, to preserve the life or health of the pregnant woman. Id. at 410 U. S. 163-164. We did not undertake in Roe to examine the various factors that may enter into the determination of viability. We simply observed that, in the medical and scientific communities, a fetus is considered viable if it is "potentially able to live outside the mother's womb, albeit with artificial aid." Id. at 410 U. S. 160. We added that there must be a potentiality of "meaningful life," id. at 410 U. S. 163, not merely momentary survival. And we noted that viability "is usually placed at about seven months (28 weeks), but may occur earlier, even at 24 weeks." Id. at 410 U. S. 160. We thus left the point flexible for anticipated advancements in medical skill. Roe stressed repeatedly the central role of the physician, both in consulting with the woman about whether or not to have an abortion and in determining how any abortion was to be carried out. We indicated that, up to the points where important state interests provide compelling justifications for intervention, "the abortion decision, in all its aspects, is inherently, and primarily, a medical decision," id. at 410 U. S. 166, and we added that, if this privilege were abused, "the usual remedies, judicial and intra-professional, are available." Ibid. Roe's companion case, Doe v. Bolton, 410 U. S. 179 (1973), underscored the importance of affording the physician adequate discretion in the exercise of his medical judgment. After the Court there reiterated that "a pregnant woman does not have an absolute constitutional right to an abortion on her demand," id. at 410 U. S. 189, the Court discussed, in a vagueness attack context, the Georgia statute's requirement that a physician's decision to perform an abortion must rest upon "his best clinical judgment." The Court found it critical that that judgment "may be exercised in the light of all factors -- physical, emotional, psychological, familial, and the woman's age -- relevant to the wellbeing of the patient." Id. at 410 U. S. 192."