Abstract
OBJECTIVES: To investigate the association between maternal early pregnancy body mass index (BMI) and offspring bipolar disorder (BPD). METHODS: We conducted a nationwide cohort study among 1,507,056 non-malformed singleton live-births in Sweden born 1983-2004. Using national registries with prospectively recorded information, we followed participants for a BPD diagnosis from ages 13 to up to 35 years. We compared BPD risks by early pregnancy BMI using hazard ratios (HR) with 95% confidence intervals (CI) from adjusted Cox models. We also conducted sibling-controlled analyses among 874,047 full siblings. RESULTS: There were 9970 BPD diagnoses. Risk of BPD was 0.72% through 25 years of age. Maternal early pregnancy BMI was positively associated with offspring BPD risk. Compared with normal BMI (18.5-24.9), adjusted HR (95% CI) for overweight (BMI 25-29.9), obesity grade 1 (BMI 30-34.9), and obesity grades 2-3 (BMI ≥35) were 1.08 (1.02, 1.15), 1.26 (1.14, 1.40), and 1.31 (1.07, 1.60), respectively. Adjusted HR per unit BMI was 1.015 (95% CI 1.009, 1.021). A similar trend was observed among siblings. Pregnancy and neonatal complications did not substantially mediate the association between maternal obesity (BMI ≥30) and offspring BPD. CONCLUSIONS: Maternal BMI ≥25 is associated with offspring BPD risk in a dose-response manner.