Background

In its landmark 1973 abortion cases, the U.S. Supreme Court held that a woman’s right to an abortion is not absolute and that states may restrict or ban abortions after fetal viability, provided that their policies meet certain requirements. In these and subsequent decisions, the Court has held that 

• even after fetal viability, states may not prohibit abortions “necessary to preserve the life or health” of the woman; 
• “health” in this context includes physical and mental health;
• only the physician, in the course of evaluating the specific circumstances of an individual case, can define what constitutes “health” and when a fetus is viable; and 
• states may not require additional physicians to confirm the attending physician’s judgment that the woman’s life or health is at risk in cases of medical emergency.

Although the vast majority of states restrict later-term abortions, many of these restrictions have been struck down. Most often, courts have voided the limitations because they do not contain a health exception; contain an unacceptably narrow health exception; or do not permit a physician to determine viability in each individual case, but rather rely on a rigid construct based on specific weeks of gestation or trimester. 

Nonetheless, statutes conflicting with the Supreme Court’s requirements remain on the books in some states. For example, the law in Michigan permits a postviability abortion only if the woman’s life is endangered and laws in several other states ban abortion at a specific point in gestation. Most recently, several states have enacted laws that ban abortion at 20 weeks’ postfertilization—well before viability—based on the spurious assertion that a fetus can feel pain at that point. Dating a pregnancy from fertilization goes against convention. When discussing pregnancy, medical professionals customarily date a pregnancy from the first day of the woman’s last menstrual period, because that is the date most women can pinpoint.  Fertilization commonly takes place two weeks after the first day of a woman’s last menstrual period. Accordingly, a pregnancy of normal gestational length is considered to last approximately 40 weeks from the beginning of a woman’s last menstrual period—or 38 weeks’ postfertilization.