At the heart of liberty is the right to define one's own concept of existence, of meaning, of the universe, and of the mystery of human life.... people have organized intimate relationships and made choices that define their views of themselves and their places in society, in reliance on the availability of abortion in the event that contraception should fail.... We conclude the line should be drawn at viability, so that, before that time, the woman has a right to choose to terminate her pregnancy.... there is no line other than viability which is more workable. To be sure, as we have said, there may be some medical developments that affect the precise point of viability, but this is an imprecision within tolerable limits.... A husband has no enforceable right to require a wife to advise him before she exercises her personal choices.