Miscarriage is a common event in pregnancy. Most early losses stem from genetic abnormalities, and thus the opportunity for prevention is small. Women with later miscarriage or with recurrent miscarriage more likely have a chronic etiology that may be modified. In contrast to these spontaneous losses, pregnancy termination may be elected. For both induced abortion and miscarriage, management options include surgery or medication, and providers should have an understanding of these methods and their potential complications.
Abortion is defined as the spontaneous or induced termination of pregnancy before fetal viability. Many prefer miscarriage for spontaneous loss. Induced abortion describes termination with surgery or medication of a live fetus that has not reached viability.
Definitions of an abortus vary among organizations. The National Center for Health Statistics and the World Health Organization define abortion as loss or termination of a pregnancy with a fetus aged younger than 20 weeks’ gestation or weighing <500 g. These criteria, however, are somewhat contradictory because the mean birthweight of a 20-week fetus approximates 330 g, whereas 500 g is the mean for 22 weeks (Hadlock, 1991). Further confusion may derive from criteria that are set by state laws and define abortion even more widely.
Incongruity also exists for the term early pregnancy loss itself. The American College of Obstetricians and Gynecologists (2019b) defines this as a nonviable, intrauterine pregnancy (IUP) within the first 126/7 weeks of gestation that consists of either an empty gestational sac or one containing an embryo or fetus without fetal heart activity. Recurrent pregnancy loss is variably defined but is meant to identify women with repetitive miscarriage (p. 203).
Other definitions help distinguish intrauterine from ectopic gestations. The term pregnancy of unknown location (PUL) describes a pregnancy identified by human chorionic gonadotropin (hCG) level testing but without a confirmed sonographic location. In this context, five categories are proposed for early pregnancies: definite ectopic pregnancy, probable ectopic pregnancy, PUL, probable IUP, and definite IUP (Barnhart, 2011). Diagnostic and management options for ectopic gestation are described in Chapter 12.
Last, spontaneous abortion includes subcategories of threatened, incomplete, complete, missed, and inevitable abortions. These are discussed in the next sections. Septic abortion is used to further classify any of these that are complicated by infection.
FIRST-TRIMESTER SPONTANEOUS ABORTION
More than 80 percent of spontaneous abortions occur within the first 12 weeks of gestation. With first-trimester losses, demise 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 stimulates uterine contractions and expulsion. An intact gestational sac is usually filled with fluid. Anembryonic miscarriage or preembryonic loss describes the group with no identifiable embryo. The term blighted ovum is less preferred. An embryonic ...