Abortion, Placentas of Trisomies, and Immunological Considerations of Recurrent Reproductive Failure

Abstract

For the present discussion, an abortion or miscarriage is designated a conceptus that is expelled before the 20th week of gestation. That is important to state at the outset, as the pathological features of failed pregnancies differ markedly in specimens obtained later in gestation. In the United States, terminations before 20 weeks constitute abortions; later gestations are premature deliveries. A pregnancy of 20 weeks is legally at the dividing line; it is considered a gestation with an “embryo” (which may be treated as a surgical specimen) or, later, with a “fetus,” whose examination constitutes an autopsy. The terminology employed in publications and statistics differs widely and is not the same in different countries. For example, Vogel in Germany (1969, 1992) considered an abortion to be an expelled fetus of less than 1,000 g. He differentiated between embryonic and fetal (15–28 weeks) abortion. In many countries, legal viability is considered to be attained only at 28 weeks of gestation when the fetus has attained approximately 1,000 g in weight, but that is not so in the United States. Byrne et al. (1985), in a study of early fetal deaths, considered all specimens less than 28 weeks gestation. For these reasons, it is difficult to place the studies of Vogel (1969, 1992) into context with current terminology. Hutchon (1998) reviewed the complex terminology of this topic and proposed (with concurrence of a British Study Group on terminology) that the term abortion be replaced with miscarriage for all types under discussion. Most truly spontaneous abortions occur before 12 weeks of gestation and most result from chromosomal errors in the conceptus. Relatively few really spontaneous abortions occur between 12 and 20 weeks of gestation. Thereafter, between 20 and 30 weeks, another type of premature spontaneous termination becomes prevalent, that which is primarily caused by ascending infection with chorioamnionitis; infection is relatively uncommon before 20 weeks. These types of termination are fundamentally different processes with vastly different pathological findings.