Late termination of pregnancy, also referred to politically^{[clarification needed]} as third trimester abortion, describes the termination of pregnancy by inducing labor during a late stage of gestation. In this context, late is not precisely defined, and different medical publications use varying gestational age thresholds. As of 2015, in the United States, more than 90% of abortions occur before the 13th week, 1.3% take place after the 21st week, and less than 1% occur after 24 weeks.

Reasons for late terminations of pregnancy include circumstances where a pregnant woman's health is at risk or when birth defects, such as lethal fetal abnormalities, have been detected.

In the United States, the mortality rate for legal abortions overall is less than 1 in 100,000 procedures performed. The rate of mortality and morbidity increases with the gestational age of the fetus, so patients who have decided to have an abortion are strongly encouraged to get it early. Still, later abortion is not associated with any greater net negative physical or mental health outcomes (including mortality) than full-term pregnancy and childbirth in the United States.

Late termination of pregnancy is more controversial than abortion in general. All countries in Europe do not permit abortion later in pregnancy (after 10-14 weeks in most countries, 18 weeks in Sweden and Iceland, and 24 weeks in the Netherlands and the United Kingdom) unless specific circumstances are present, generally when the pregnancy represents a serious danger to the life, or to the physical or mental health of the woman, or when a serious malformation or anomaly of the fetus is diagnosed.

A late termination of pregnancy often refers to an induced ending of pregnancy after the 20th week of gestation, i.e. after a fetal age (time since conception) of about 18 weeks. The exact point when an abortion is considered late-term, however, is not clearly defined. In three articles published in 1998 in the same issue of the Journal of the American Medical Association (JAMA), two chose the 20th week of gestation and one chose the 28th week of gestation as the point where an abortion procedure would be considered late-term.

In the United States, the point at which an abortion becomes late-term is often related to fetal viability (ability of the fetus to survive outside the uterus). Thus, late-term abortions are sometimes referred to as post-viability abortions.

There is no sharp limit of development, age, or weight at which a fetus becomes viable. A 2015 study found that even with active treatment, no infants born at less than 22 weeks survived, but an infant born at 21 weeks and one day in April of 2021 did survive his premature birth. At 23 weeks survival without severe impairment is less than 2%, and at 25 weeks, up to 30% might survive without severe impairment. According to studies between 2003 and 2005, 20 to 35 percent of babies born at 24 weeks of gestation survived, while 50 to 70 percent of babies born at 25 weeks, and more than 90 percent born at 26 to 27 weeks, survived. Because the chance of survival is variable based on interventions available and the weight and sex of the fetus, there is no consensus on viability. The American College of Obstetricians and Gynecologists reports that 23% of abortion providers offer abortions at 20 weeks of gestation and later, most often using a method called dilation and evacuation (D&E).

Reasons for late terminations of pregnancy include when a pregnant woman's health is at risk or when lethal fetal abnormalities have been detected.