The United States Supreme Court decisions on abortion, including Roe v. Wade, allow states to impose more restrictions on post-viability abortions than during the earlier stages of pregnancy.
As of April 2007, 36 states had bans on late-term abortions that were not facially unconstitutional (i.e. banning all abortions) or enjoined by court order. In addition, the Supreme Court in the case of Gonzales v. Carhart ruled that Congress may ban certain late-term abortion techniques, "both previability and postviability".
The Supreme Court has held that bans must include exceptions for threats to the woman's life, physical health, and mental health, but four states allow late-term abortions only when the woman's life is at risk; four allow them when the woman's life or physical health is at risk, but use a definition of health that pro-choice organizations believe is impermissibly narrow. Assuming that one of these state bans is constitutionally flawed, then that does not necessarily mean that the entire ban would be struck down: "invalidating the statute entirely is not always necessary or justified, for lower courts may be able to render narrower declaratory and injunctive relief."
Also, 13 states prohibit abortion after a certain number of weeks' gestation (usually 24 weeks). The U.S. Supreme Court held in Webster v. Reproductive Health Services that a statute may create "a presumption of viability" after a certain number of weeks, in which case the physician must be given an opportunity to rebut the presumption by performing tests. Therefore, those 13 states must provide that opportunity. Because this provision is not explicitly written into these 13 laws, as it was in the Missouri law examined in Webster, pro-choice organizations believe that such a state law is unconstitutional, but only "to the extent that it prohibits pre-viability abortions".
Ten states require a second physician to approve. The U.S. Supreme Court struck down a requirement of "confirmation by two other physicians" (rather than one other physician) because "acquiescence by co-practitioners has no rational connection with a patient's needs and unduly infringes on the physician's right to practice". Pro-choice organizations such as the Guttmacher Institute therefore interpret some of these state laws to be unconstitutional, based on these and other Supreme Court rulings, at least to the extent that these state laws require approval of a second or third physician.
Nine states have laws that require a second physician to be present during late-term abortion procedures in order to treat a fetus if born alive. The Court has held that a doctor's right to practice is not infringed by requiring a second physician to be present at abortions performed after viability in order to assist in saving the life of the fetus.