pregnancy and the postpartum period are a vulnerable time for the onset of obesity, especially in primiparous (first-time) mothers. because postpartum weight retention is a strong independent risk factor for chronic disease, in addition to lifetime obesity with compounded risk for maternal/fetal complications in subsequent pregnancies, a need for lifestyle interventions promoting weight loss and health among primiparous mothers exists. motivational interviewing-via-co-active life coaching (mi-via-calc) has shown significant results relating to evoking health behaviour change and weight loss in adults with obesity. however, no studies have explored the utility of mi-via-calc as an intervention in primiparous women – a challenging population to reach due to competing demands and new responsibilities. as a cognitive-behavioural technique delivered over the telephone, mi-via-calc may be optimal in this regard. the co-active model has been previously grounded in self-determination theory (sdt), which focuses on the concept of motivation. given the similarities between the tenets of sdt and mi-via-calc, and the notion that mi-via-calc could support sdt’s basic psychological needs (i.e., autonomy, competence, and relatedness), the use of this health behaviour change method in an intervention study has been recommended.