PIP: The most common specimen from induced abortions comes from suction curettages; least commonly found are future hydatidiform moles found in this material. In specimens obtained after the instillation of hypertonic solutions, the embryo is usually macerated and chromosomal studies are limited to villous tissue and are difficult. The placenta, however, shows characteristic changes of coagulation necrosis of the chorionic plate and a narrow superficial portion of villous tissue. In specimens from early spontaneous abortions, chromosomal anomalies of the conceptus make up the majority; after week 12 of pregnancy molar changes become more frequent and the incidence of aneuploidy decreases. Chromosomal errors are now thought to account for at least 50% of spontaneously aborted fetuses. In families with 2 or more spontaneous abortions it is recommended that detailed bending cytogenetic study of both parents should be performed. Pathologic findings on spontaneous abortion material are extremely varied; the most deformed embryos are due to major chromosomal errors. The anatomic features of the embryo are more easily understood than the placental changes of spontaneous abortions and include chorioamnionitis, hostile uterine environment with retroplacental hematoma, endometritis, and Breus' mole. The latter occurs when masses of clot and fibrin accumulate beneath the chorionic surface, projecting focally into the cavity whose normal content has possibly deflated after fetal death. The most difficult task is the interpretation of the villous changes of spontaneous abortions; of these the most difficult are the transitional or partial moles. A recent discovery is that moles have an androgenic origin. Moles fall into 2 categories, true hydatidiform moles with diploid chromosomes and partial moles. It has been suggested that true moles do not possess embryos and are never in a transitional stage, while partial moles are more commonly aneuploid and have irregularly distributed fluid engorgement, sparing many villi. Moles of both types have elevated gonadotropin titres and both are often complicated by severe preeclampsia. Somewhat different factors are exhibited in pregnancies where large fetuses accompany moles.