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The classification and mechanisms of spontaneous abortion.

This classification of spontaneous abortions, based on placental rather than embryonic or fetal morphology, does not entail detailed embryological or histological techniques. It is readily adaptable to routine pathological laboratory practice. The advantages that may accrue from proper examination of spontaneous abortions are numerous and include provision of both clinical and epidemiological data pertinent to the immediate management of the aborting patient, as well as basic information that may clarify the mechanisms underlying the major complications of pregnancy which contribute to perinatal mortality in developed societies. The pathology of the placenta in groups 1 and 2 is seen as a possible indicator of the mechanisms leading to spontaneous abortions in man. The lesions are not seen in isolation but are viewed as a logical progression related to the time at which normal development ceases. The key and unifying concept in the hypothesis is the role of the villous circulation in the maintenance of normal trophoblastic function. In the earliest abortions, the villous circulation never develops, resulting in microscopic hydatidiform or hydropic change within the villus and attenuation of the trophoblast, while embryonic or fetal death following the establishment of a villous circulation results in the sequential changes characteristic of group 2 cases. Although the majority of embryonic and fetal deaths still remain unexplained, the hypothesis suggests a mechanism by which the abnormal conceptus may determine the outcome of pregnancy without invoking the concept of maternal rejection. Verification and extension of this hypothesis will require correlation of clinical, endocrinological, and morphological data. The histopathologist has failed to keep pace with advances in modern obstetrics during the last decade, particularly in the field of early pregnancy wastage, thus reinforcing the clinical opinion that morphological examination of abortions has little to offer in the clinical management of these cases. If counseling and therapy are to be based on scientific concepts rather than on empirical data, it is essential that this deficiency be rectified.