Coparenting-focused preventive intervention reduces postnatal maternal BMI and buffers impact of cortisol

Objective: The postpartum period is a key life stage, contributing to increased maternal obesity risk. Current lifestyle interventions do not consider the role of a woman's partner in reducing stress and supporting lifestyle change. The objective of this study was to assess the effect of an intervention that seeks to enhance coparenting relationship quality on maternal BMI from before conception to 12 months post partum and whether the intervention moderated the association of changes in cortisol and BMI. Methods: A randomized controlled trial was used to assess an intervention (eight classes: four during and four following pregnancy) focusing on enhancing couple coparenting relationships during pregnancy and post partum (n = 57) compared with standard care (n = 53). Results: The main outcome measures were changes in maternal BMI and cortisol. There was a smaller increase in BMI for mothers in intervention compared with control groups (mean [SE], −1.03 [0.42] kg/m², p = 0.015). There was an interaction between intervention status and cortisol change predicting BMI change (p = 0.026), such that cortisol change significantly predicted BMI change among mothers in the control (p = 0.049) but not the intervention groups (p = 0.204). Conclusions: A coparenting intervention improved maternal postpartum BMI, with this effect potentially related to ameliorating the negative effect of stress, as measured by cortisol, on BMI. The role of enhanced coparenting in improving maternal anthropometry warrants urgent attention.