Once pregnancy is recognized clinically, it is accepted that 12% to 15% undergo spontaneous abortion. However, the actual time of fetal demise has not yet been determined. To address this question, the outcomes of pregnancies identified before 21 days of conception by serum β-human chorionic gonadotropin assays were studied. All subjects underwent ultrasound examinations at eight and 12 weeks' gestation. Among 220 women who had a viable pregnancy at eight weeks, only seven (3.2%) experienced a fetal loss thereafter. The results of this study suggest that most clinically recognized spontaneous abortions manifested after eight weeks actually represent pregnancies in which fetal demise occurred before eight weeks. These findings have important implications with respect to the safety of chorionic villi sampling and to the identification of exogenous agents that cause fetal wastage.