Measurements of human chorionic gonadotropin (hCG) have been used to assess early embryo loss in women. Urine samples obtained from a control group of sterilized women with normal ovulatory menstrual cycles enabled a concentration limit of 56 IU/l to be determined so that any nontrophoblastic hCG or other cross-reacting compounds could be accounted for. One hundred ninety-eight ovulatory cycles were collected from a normal population attempting to conceive. Fecundability was 22% to 27% for this population. The risk of pregnancy in exposed ovulatory cycles was 59.6%; however, 61.9% of conceptuses will be lost prior to 12 weeks. Most of these losses (91.7%) occur subclinically, without the knowledge of the mother.