Advances in early fetal loss research: importance for risk assessment.

The assessment of early fetal losses (EFLs) in relationship to environmental agents offers unique advantages compared to other end points for hazard assessment. There is a high incidence (greater than 20% of all pregnancies end in an EFL), and the interval between exposure and end point is the short duration between conception and event, i.e., approximately 12 weeks. In contrast, cancer, which is the primary end point evaluated in risk assessment models, occurs with much lower frequency, and the latency period is measured in years or decades. EFLs have not been used effectively for risk assessment because most of the events are not detected. Prospective studies provide the only approach whereby it is possible to link exposure to EFLs. Recent methodologic advancements have demonstrated that it is now possible to conduct population-based studies of EFLs. It is likely that EFLs could serve as sentinels to monitor adverse health effects of many potential environmental hazards. The methodology will be demonstrated using lead exposure in utero as an example.