Mothers' and partners' changes in health behaviours during pregnancy: observations from the Growing Up in New Zealand Cohort.

Improving modifiable health behaviours during pregnancy may benefit parental health and offspring outcomes. Although pregnancy may motivate lifestyle change in both mothers and partners, evidence on partner health behaviour change and within-couple alignment remains limited. Antenatal data from the Growing Up in New Zealand cohort were used to describe health behaviour changes among mothers (n = 6822) and partners (n = 4401), and to examine associations between selected dietary changes within mother-partner dyads (n = 1195). Measures included changes in physical activity, alcohol use, smoking, and diet [avoidance of sugar-sweetened beverages (SSBs) and fast foods, and the addition of fruits and vegetables]. Associations were examined using multivariate Poisson regression models with robust variance. Most mothers (73.7%) remained consistently active or inactive during pregnancy, while 43.4% of partners reported changes in activity. Around 43% of both mothers and partners reduced or stopped alcohol use. Nearly half of smoking mothers quit, and two-thirds of smoking partners reduced or quit smoking. For diet, 22.9% and 30.7% of mothers avoided SSBs and fast foods, respectively, and 15.8% added fruits and/or vegetables; respective figures for partners were 13.2%, 9.9%, and 19.2%. Significant dyadic associations were observed for avoiding SSBs (Prevalence ratio [PR]: 1.37, 95% confidence interval [CI]: 1.04-1.79) and for adding fruits and/or vegetables to diets (PR: 2.05, 95% CI: 1.59-2.65). These findings indicate that pregnancy may represent a shared context for health behaviour change within households and highlight the potential value of partner-inclusive antenatal approaches.