ABSTRACT
This chapter aims to sketch the biological processes of early pregnancy, to acquaint the reader with some of the historically important epidemiologic studies in this area, and to speculate on opportunities that medical technology may bring to the epidemiologic study of early pregnancy. The single most useful marker in reproductive epidemiology would be a marker of conception — the elusive denominator. The opportunities for exploring biological mechanisms of conception and implantation among Early pregnancies are startling. For example, it would be possible in principle to study the prevalence of gene abnormalities among fertilized eggs. The beating embryonic heart can be detected by five weeks after conception. The chapter describes the epidemiology of early human pregnancy as largely uncharted territory. The pregnant women is usually unaware of her own pregnancy during the first three weeks after conception, by which time the conceptus has already formed the primordial germ cells of the next generation.
