The word abortion derives from the Latin aboriri—to miscarry. Abortion is defined as the spontaneous or induced termination of pregnancy before fetal viability. It thus is appropriate that miscarriage and abortion are terms used interchangeably in a medical context. But because popular use of abortion by laypersons implies a deliberate intact pregnancy termination, many prefer miscarriage for spontaneous fetal loss. Newer terms made possible by widespread use of sonography and human chorionic gonadotropin measurements that identify extremely early pregnancies include early pregnancy loss, wastage, or failure. Throughout this book, these are all used at one time or another.
Terminology used to define fetal viability and thus an abortus has tremendous medical, legal, and social import. Viability lies between the lines that separate abortion from preterm birth. It is usually defined by pregnancy duration and fetal birthweight for statistical and legal purposes (Chap. 1, Vital Statistics). This has led to incongruities in definitions from authoritative organizations. Importantly, the National Center for Health Statistics, the Centers for Disease Control and Prevention, and the World Health Organization all define abortion as pregnancy termination before 20 weeks' gestation or with a fetus born weighing < 500 g. These criteria, however, are somewhat contradictory because the mean birthweight of a 20-week fetus is 320 g, whereas 500 g is the mean for 22 to 23 weeks (Moore, 1977). Further confusion may derive from criteria set by state laws that define abortion even more widely.
As indicated above, technological developments have revolutionized current abortion terminology. Transvaginal sonography (TVS) and precise measurement of serum human chorionic gonadotropin (hCG) concentrations are used to identify extremely early pregnancies as well as those with an intrauterine versus ectopic location. Ubiquitous application of these practices makes it possible to distinguish between a chemical and a clinical pregnancy. An ad hoc international consensus group has proposed the term pregnancy of unknown location—PUL—with the goal of early identification and management of ectopic pregnancy (Barnhart, 2011; Doubilet, 2013). Management options for ectopic gestation are described in Chapter 19 (Medical Management). Uterine pregnancies that eventuate in a spontaneous abortion are also termed early pregnancy loss or early pregnancy failure.
Terms that have been in clinical use for many decades are generally used to describe later pregnancy losses. These include:
Spontaneous abortion—this category includes threatened, inevitable, incomplete, complete, and missed abortion. Septic abortion is used to further classify any of these that are complicated further by infection.
Recurrent abortion—this term is variably defined, but it is meant to identify women with repetitive spontaneous abortions so that an underlying factor(s) can be treated to achieve a viable newborn.
Induced abortion—this term is used to describe surgical or medical termination of a live fetus that has not reached viability.
First-Trimester Spontaneous Abortion
More than 80 percent of spontaneous abortions occur within the first 12 weeks of gestation. With first-trimester losses, death of the embryo or fetus nearly always precedes spontaneous expulsion. Death is usually accompanied by hemorrhage into the decidua basalis. This is followed by adjacent tissue necrosis that ...