Seasonality of schizophrenia and stillbirths.

A study of the birth pattern of 30,467 patients with schizophrenia and 428,406 stillbirths in New York State showed a significant winter-month excess in both schizophrenia births (p = 0.0000) and stillbirths (p = 0.0000). Excess births of individuals with schizophrenia in November and December provided additional evidence to refute the age-incidence explanation for the observed seasonality. Time series spectral analysis showed coherence in the pattern of schizophrenia births and stillbirths of 0.898 (p < 0.003) with schizophrenia births preceding stillbirths by 13 days. These results suggest that a common etiological seasonal factor affects a subgroup of births of individuals who later develop schizophrenia and a subgroup of stillbirths. Nutritional factors, temperature, and infectious agents known to cause both central nervous system disease and stillbirths are possible candidates.