Time trends in schizophrenia: changes in obstetric risk factors with industrialization.

The frequency of schizophrenia may have increased during the early stages of industrialization and may now be declining. Early in the process of development, the illness appeared to be more common among the upper classes and later, more common in the lower classes. As with certain other diseases, the occurrence of schizophrenia may be influenced by the transition from poverty to affluence. Explanations for such a pattern of occurrence include the combined effect of (1) variation in the rate of birth complications owing to cephalopelvic disproportion secondary to changes in nutrition, and (2) increased infant survival following improvements in obstetric and neonatal care. These effects help elucidate the pattern of occurrence of schizophrenia in immigrant groups.