Roe v. Wade
In its decision, the court used the three-trimester framework of pregnancy. During the first trimester, an abortion was safer for the mother than childbirth. The reasoning was that the decision of whether to get an abortion at that stage should be left up to the mother to decide. Any law that interfered with abortions in the first trimester would be presumed to be unconstitutional. During the second trimester, laws could regulate abortion only to protect the health of the mother. During the third trimester, the unborn child was viable and so could live on its own, outside the mother's womb. Then, laws could restrict or prohibit abortions unless it was necessary to preserve the mother's health. That doctrine stood until 1992, when Planned Parenthood v. Casey had the court now base the legality of an abortion no longer on trimesters but on fetal viability.