Objective: Winter birth has consistently been identified as a risk factor for schizophrenia. This study aimed to determine whether individuals born during this season are also at higher risk for early psychosis and whether this is associated with distinct functional and clinical outcomes.

Methods: We conducted a prospective study on 222 patients during their early phase of psychosis in Switzerland, nested in the Treatment and Early Intervention in Psychosis (TIPP) cohort. We compared the birth trimesters of these patients with those of the general Swiss population. Additionally, we evaluated the Global Assessment of Functioning scale (GAF) and the Positive and Negative Syndrome Scale (PANSS) scores among patients born in winter (January to March) versus those born during the rest of the year during a three-year follow-up period.

Results: A significantly higher proportion of patients experiencing early psychosis were born in winter compared to the general Swiss population. Patients born in winter had significantly lower GAF scores at 6 months, 24 months, and 36 months of follow-up, compared to patients born during the rest of the year. They also manifested fewer positive symptoms, as indicated by the PANSS positive subscale.

Conclusion: Birth in winter appears to be associated with a lower functional outcome and potentially distinct symptomatology in the early phase of psychosis.