Since 1995, at least thirty-one states have enacted laws banning the so-called "partial-birth" abortion procedure. Although many of these laws have not taken effect because of permanent injunctions, they remain contentious to both pro-life advocates and those who support a woman's right to choose. The concern over partial-birth abortion has been shared by Congress. Congress passed bans on the partial-birth abortion procedure in both the 104 th and 105 th Congresses. Unable to overcome presidential vetoes during both congressional terms, the Partial-Birth Abortion Ban Act was reintroduced in each successive Congress until its enactment in 2003. S. 3 , the Partial-Birth Abortion Ban Act of 2003, was passed by Congress in October 2003. The measure was signed by the President on November 5, 2003. The U.S. Supreme Court has also addressed the performance of partial-birth abortions. In Stenberg v. Carhart , a 2000 case, the Court invalidated a Nebraska statute that prohibited the performance of such abortions. Prior to this decision, the U.S. Courts of Appeals remained divided on the legitimacy of state statutes banning partial-birth abortions. In Gonzales v. Carhart , a 2007 case, the Court upheld the Partial-Birth Abortion Ban Act of 2003, finding that, as a facial matter, it is not unconstitutionally vague and does not impose an undue burden on a woman's right to terminate her pregnancy. This report discusses the Court's decisions and the partial-birth abortion measures in the 106 th , 107 th , and 108 th Congresses. The Supreme Court has held that a woman has a constitutional right to choose whether to terminate her pregnancy. Although a state cannot prohibit a woman from having an abortion, it can promote its interest in potential human life by regulating, and even proscribing, abortion after fetal viability so long as it allows an exception for abortions that are necessary for the preservation of the life or health of the mother. In Planned Parenthood of Southeastern Pennsylvania v. Casey , the Court expanded a state's authority to regulate abortion by permitting regulation at the pre-viability stage so long as such regulation does not place an "undue burden" on a woman's ability to have an abortion. The term "partial-birth abortion" refers generally to an abortion procedure where the fetus is removed intact from a woman's body. The procedure is described by the medical community as "intact dilation and evacuation" or "dilation and extraction" ("D & X") depending on the presentation of the fetus. Intact dilation and evacuation involves a vertex or "head first" presentation, the induced dilation of the cervix, the collapsing of the skull, and the extraction of the entire fetus through the cervix. D & X involves a breech or "feet first" presentation, the induced dilation of the cervix, the removal of the fetal body through the cervix, the collapsing of the skull, and the extraction of the fetus through the cervix. This report uses the term "D & X" to encompass both procedures. D & X is one of several abortion methods. The principal methods of abortion are suction curettage, induction, and standard dilation and evacuation ("D & E"). The decision to perform one abortion method over another usually depends on the gestational age of the fetus. During the first trimester, the most common method of abortion is suction curettage. Suction curettage involves the evacuation of the uterine cavity by suction. The embryo or fetus is separated from the placenta either by scraping or vacuum pressure before being removed by suction. Induction may be performed either early in the pregnancy or in the second trimester. In this procedure, the fetus is forced from the uterus by inducing preterm labor. D & E is the most common method of abortion in the second trimester. Suction curettage is no longer viable because the fetus is too large in the second trimester to remove by suction alone. D & E involves the dilation of the cervix and the dismemberment of the fetus inside the uterus. Fetal parts are later removed from the uterus either with forceps or by suction. D & X is typically performed late in the second trimester between the twentieth and twenty-fourth weeks of pregnancy. Although the medical advantages of D & X have been asserted, the nature of the procedure has prompted pro-life advocates to characterize D & X as something akin to infanticide. In Women ' s Medical Professional Corporation v. Voinovich , the U.S. Court of Appeals for the Sixth Circuit discussed the differences between the D & E and D & X procedures in reference to an Ohio act that banned partial-birth abortions: The primary distinction between the two procedures is that the D & E procedure results in a dismembered fetus while the D & X procedure results in a relatively intact fetus. More specifically, the D & E procedure involves dismembering the fetus in utero before compressing the skull by means of suction, while the D & X procedure involves removing intact all but the head of the fetus from the uterus and then compressing the skull by means of suction. In both procedures, the fetal head must be compressed, because it is usually too large to pass through a woman's dilated cervix. In the D & E procedure, this is typically accomplished by either suctioning the intracranial matter or by crushing the skull, while in the D & X procedure it is always accomplished by suctioning the intracranial matter. The procedural similarities between the D & E and D & X procedures have contributed to the concern that the language of partial-birth abortion bans may prohibit both methods of abortion. Plaintiffs challenging partial-birth abortion statutes have generally sought the invalidation of such statutes on the basis of two arguments: first, that the statutes are unconstitutionally vague, and second, that the statutes are unconstitutional because they impose an undue burden on a woman's ability to obtain an abortion. The Supreme Court has held that an enactment is void for vagueness if its prohibitions are not clearly defined. Vague laws are found unconstitutional because they fail to give people of ordinary intelligence a reasonable opportunity to know what is prohibited and thus allow them to act lawfully. Moreover, the inability to provide explicit standards is feared to result in the arbitrary and discriminatory enforcement of a statute. The undue burden standard was adopted by the Court in Casey . In that case, the Court held that a state could enact abortion regulations at the pre-viability stage so long as an "undue burden" is not placed on a woman's ability to have an abortion. Any regulation which "has the purpose or effect of placing a substantial obstacle in the path of a woman seeking an abortion" creates an undue burden and is invalid. The Sixth Circuit was the first to consider whether a ban on partial-birth abortions imposes an undue burden on a woman's ability to have an abortion. In Voinovich , the court found that an Ohio statute that attempted to ban the D & X procedure was unconstitutional under Casey . The court determined that the language of the statute targeted the D & X procedure, but encompassed the D & E procedure. Because the D & E procedure is the most common method of second trimester abortions, the court contended that the statute created an undue burden on women seeking abortions at this point in their pregnancies. In Stenberg v. Carhart , a Nebraska physician who performed abortions at a specialized abortion facility sought a declaration that Nebraska's partial-birth abortion ban statute violated the U.S. Constitution. The Nebraska statute provided: No partial birth abortion shall be performed in this state, unless such procedure is necessary to save the life of the mother whose life is endangered by a physical disorder, physical illness, or physical injury, including a life-endangering physical condition caused by or arising from the pregnancy itself. The term "partial birth abortion" was defined by the statute as "an abortion procedure in which the person performing the abortion partially delivers vaginally a living unborn child before killing the unborn child and completing the delivery." The term "partially delivers vaginally a living unborn child before killing the unborn child" was further defined as "deliberately and intentionally delivering into the vagina a living unborn child, or a substantial portion thereof, for the purpose of performing a procedure that the person performing such procedure knows will kill the unborn child and does kill the unborn child." Violation of the statute carried a prison term of up to twenty years and a fine of up to $25,000. In addition, a doctor who violated the statute was subject to the automatic revocation of his license to practice medicine in Nebraska. Among his arguments, Dr. Carhart maintained that the meaning of the term "substantial portion" in the Nebraska statute was unclear and thus, could include the common D & E procedure in its ban of partial-birth abortions. Because the Nebraska legislature failed to provide a definition for "substantial portion," the U.S. Court of Appeals for the Eighth Circuit interpreted the Nebraska statute to proscribe both the D & X and D & E procedures: "if 'substantial portion' means an arm or a leg - and surely it must - then the ban ... encompasses both the D & E and the D & X procedures." The Eighth Circuit acknowledged that during the D & E procedure, the physician often inserts his forceps into the uterus, grasps a part of the living fetus, and pulls that part of the fetus into the vagina. Because the arm or leg is the most common part to be retrieved, the physician would violate the statute. The state argued that the statute's scienter or knowledge requirement limited its scope and made it applicable only to the D & X procedure. According to the state, the statute applied only to the deliberate and intentional performance of a partial birth abortion; that is, the partial delivery of a living fetus vaginally, the killing of the fetus, and the completion of the delivery.