Mental health and body mass index in early pregnancy: a secondary analysis of three randomised controlled trials.

OBJECTIVE: Overweight and obesity in pregnant women have been associated with an increased risk of depression and anxiety, but the strength of these associations and the influence of confounders remain uncertain. Understanding these associations may help identify women at risk in early pregnancy and guide targeted support. This study aimed to quantify associations between maternal body mass index (BMI) and symptoms of depression, anxiety, and health-related quality of life (HRQoL) in early pregnancy and to assess whether they persisted after adjustment for confounders. METHODS: This secondary analysis pooled baseline data from three randomised controlled trials including women at gestational week 10 + 0 to 20 + 0: LIMIT (BMI ≥ 25.0 kg/m²), GRoW (BMI ≥ 25.0 kg/m²) and OPTIMISE (BMI ≥ 18.5 to ≤ 24.9 kg/m²). LIMIT and OPTIMISE randomised participants to lifestyle intervention or standard care. In GRoW all women received a lifestyle intervention and were randomised to metformin or placebo. At baseline, women completed questionnaires assessing symptoms of depression, anxiety, and HRQoL (SF-12 or SF-36). RESULTS: 2961 pregnant women (mean BMI: 29.3 kg/m2; mean age: 30.1 years) completed at least one questionnaire, including 1815 (61%) from LIMIT, 513 (17%) from GRoW, and 633 (21%) from OPTIMISE. Higher BMI was associated with an increase in depressive and anxiety symptoms in unadjusted analyses. After adjustment, only the association with depressive symptoms remained significant (β = 0.05, 95% CI 0.02, 0.08). BMI was inversely associated with physical HRQoL (βSF-12=-0.36, 95% CI -0.45, -0.27; βSF-36=-0.18, 95% CI -0.25, -0.11). Mental HRQoL was positively associated with BMI using SF-12 (βSF-12 = 0.18, 95% CI 0.08, 0.29) but showed no association with BMI using SF-36 (βSF-36=-0.07, 95% CI -0.15, 0.02). CONCLUSION: Increasing BMI was associated with higher depressive symptoms and poorer physical HRQoL in early pregnancy, but effect sizes were small, inconsistent, and attenuated after adjustment, suggesting modest associations partly explained by confounding. These findings highlight the need for a holistic approach to supporting mental health in pregnant women with overweight or obesity, as multiple factors beyond body weight likely contribute. TRIAL REGISTRATION: Australian New Zealand Clinical Trials Registry; LIMIT (ACTRN12607000161426, 9 March 2007); OPTIMISE (ACTRN12614000583640, 30 May 2014); GRoW (ACTRN12612001277831, 10 December 2012).