ABSTRACT
Gestational and perinatal lethality is a common occurrence in mice following deliberate genetic engineering or exposure to toxicants. In many research programs, pathology evaluation of lethal phenotypes is conned to morphologic assessment for gross and microscopic defects. Unfortunately, investigations limited to structural evaluations often are unrewarding because many lethal phenotypes result from complicated physiologic abnormalities that do not manifest as anatomic lesions. As a result, a cause for any deaths that occur during the embryonic, fetal, or perinatal stages of development often remains undetermined.
