ABSTRACT
Our growing understanding of gestational biology indicates that many major clinical complications of pregnancy, including implantation failure, embryonic lethality (spontaneous abortion), intrauterine restriction of fetal growth, and preeclampsia (placental ischemia), are consequences of primary placental lesions in both animals and humans. In particular, embryo lethality in mice often results from placental dysfunction rather than abnormalities in the embryo. However, placental damage is often missed by investigators. This aw in many mouse developmental pathology studies results from three major errors. The rst is a narrow analytical focus that is limited to identifying and characterizing the changes that occur in the embryo or fetus. In such cases, the extraembryonic elements are entirely ignored. The second mistake is to evaluate the placenta in a cursory fashion, noting the presence of a placental abnormality in general terms (e.g., describing the specimen as hemorrhagic or pale or small) without seeking to rigorously dene the lesions responsible for the change at the tissue and cellular levels. The nal error is to delegate the task of placental analysis to an individual with little theoretical knowledge or practical experience in mouse developmental pathology. In our research careers, many studies incorporate two or even all three of these design aws.
