Seasonality of Birth among Patients with Schizophrenia at Saint Paul’s and Amanuel Mental Specialized Hospitals, Ethiopia: A Cross-sectional Study

Abstract

Abstract Background: Birth of birth has been implicated as a potential risk factor for schizophrenia, suggesting the influence of environmental exposures acting during critical periods of neurodevelopment. This study aimed to assess the distribution of birth months/seasons among patients with schizophrenia compared to the general population and whether a seasonal pattern differs between genders. Methods: An institution based cross-sectional study was conducted by interviewing patients from two hospitals in Ethiopia. 496 patients with schizophrenia met the eligibility criteria and were included in the study. Monthly and seasonal birth distributions were described, and seasonality was assessed using the Walter-Elwood test. The observed monthly distribution was compared with the expected national birth distribution derived from Ethiopian Demographic and Health Survey (EDHS) referenced data using a chi square goodness-of-fit test. Associations between selected peak birth periods and sex or family history of schizophrenia were examined using chi-square tests. Results: The highest proportion of patients were born in May (11.3%), followed by January and December (each 10.9%). Births were most frequent during the Bega season (37.9%). The Walter–Elwood test demonstrated a statistically significant cyclical seasonal pattern in birth months (F (2,493) = 21.56, p < 0.001). Comparison with the general population showed a significant difference between observed and expected monthly birth distributions (χ² (11) = 27.29, p = 0.004), with excess births observed in late spring and early summer. Birth in the peak month of May was significantly associated with female sex (p = 0.002). No statistically significant associations were found between season of birth and sex or family history of schizophrenia. Conclusion: This study demonstrates a significant seasonal pattern of birth among patients with schizophrenia in Ethiopia, with an excess of births occurring in late spring and early summer. These findings support the hypothesis that seasonally varying environmental factors may contribute to schizophrenia risk. Further population-based studies are warranted to explore underlying mechanisms. Keywords: Schizophrenia, season of birth, birth month, seasonality, Walter-Elwood, Ethiopia