States may not prohibit abortion but that the states may regulate abortion as long as they do not create an undue burden on the ability to obtain an abortion. undue burden - if the regulation has the purpose or effect of placing a substantial obstacle in the path of a woman seeking a pre-viability abortion right to obtain abortion before viability (no right to ban pre-viability abortions) state has power to restrict abortion after fetal viability if it provides exceptions for pregnancies which endanger a woman's right of health state has legitimate interest from outset of pregnancy of protecting health of woman and life of fetus