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 whether to get an abortion at this 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 (able to live on its own outside the mother's womb). So laws could restrict or prohibit abortions except in cases where it was necessary to preserve the mother's health. This doctrine stood until 1992. In "Planned Parenthood v. Casey" (1992) the court changed from basing the legality of an abortion on trimesters to basing it on fetal viability.