In its landmark 1973 abortion cases, the U.S. Supreme Court recognized a constitutional right to abortion but held that states could prohibit abortion after fetal viability—the point at which a fetus can sustain life outside the uterus—if their policies met certain requirements. Since then, the Supreme Court has consistently reaffirmed the fundamental right to abortion while also allowing new limits on an individual’s ability to obtain one. However, after President Trump appointed three conservative justices, the Court now has an anti-abortion majority.

The current U.S. Supreme Court standard holds that states may prohibit abortion after fetal viability as long as there are exceptions for the life and health (both physical and mental) of the pregnant person. Under this legal standard, viability—which can range from 24 to 28 weeks after the start of the person’s last menstrual period (LMP)—must be determined on an individual basis, and determinations of both fetal viability and the patient’s health are at the discretion of the patient’s physician. Additionally, states may not require that additional physicians confirm an attending physician’s judgment that the patient’s life or health is at risk in cases of medical emergency.

The Court’s requirements place decisions regarding the timing and circumstances of an abortion in the hands of the patient and, after viability, their doctor. Most states restrict abortion at a specific point during pregnancy, which normally lasts 40 weeks LMP. In recent years, however, some state policymakers have attempted to provoke a Supreme Court challenge by banning abortion before viability. Federal and state courts have consistently blocked enforcement of laws that ban abortion before 13 weeks LMP, but more than a third of states have successfully implemented “20-week abortion bans.” These bans are based on the unfounded assertion that a fetus can feel pain at 20 weeks postfertilization (an estimated date of conception), equivalent to 22 weeks LMP.

Other states have enacted laws that prohibit or severely limit abortion in the second or third trimester (starting at 13 weeks and 25 weeks of pregnancy, respectively). When these measures have been challenged, courts have struck down laws with a blanket ban on abortion at a specific week or trimester, as well as those laws with extremely narrow health exceptions. However, not all of these restrictions have been challenged in court. As a result, some states still have statutes on the books that do not meet the Court’s requirements. For example, a few states have enacted previability bans, including a six-week ban in Texas and a 20-week ban in Mississippi. Some states also continue to maintain and enact new laws requiring involvement of a second physician to certify or attend the abortion under particular circumstances.

The result is a patchwork of state limitations on abortion throughout pregnancy that leaves many people unable to receive the care they need

Definitions

Last menstrual period (LMP): The beginning of pregnancy calculated from the start of the most recent menstrual period. An average pregnancy lasts approximately 40 weeks from this point.

Postfertilization: The beginning of pregnancy calculated from the date of conception; 20 weeks postfertilization is equivalent to 22 weeks LMP.

Postimplantation: The beginning of pregnancy calculated from the date of embryo implantation; 24 weeks postimplantation is equivalent to 27 weeks LMP.

General health: Defined by an individual doctor and includes the patient’s mental and emotional health.

Physical health: Applies only to the physical function of the patient’s body and may even be restricted to major bodily functions.

Viability: The point at which a fetus can sustain survival outside the uterus. Determined based on the fetus’s developmental progress and may vary by pregnancy. A fetus generally reaches viability between 24 and 28 weeks LMP.