Aim: The overall objective is to prevent unhealthy weight gain and body composition during pregnancy and in the postpartum period in vulnerable families (e.g. families on state benefit, single mothers). Specifically we aim: 1) To develop an intervention that is acceptable for vulnerable families and feasible to use for midwives, 2) To evaluate the effectiveness of this intervention in the prevention of unhealthy weight gain and psychological problems of the individual family members (mother, father, child), 3) To assess which factors are important for unhealthy weight gain in mother, father, and child.

Work plan: In the development phase of the project, two existing interventions will be adapted and aligned. The first is a smartphone-based intervention for overweight and obesity, and the second a lifestyle counselling intervention, based on motivational interviewing (this is a supportive way of talking about lifestyle changes). In addition, tools for the measurement of weight gain, body composition, lifestyle behaviour, psychological factors will be developed. In the intervention phase, two trials studies will beconducted (in Germany and Austria), to evaluate the effectiveness of the two adapted interventions, alone ortogether, in the prevention of unhealthy weight gain. The target group consists of vulnerable families, and the intervention addresses the lifestyle of both mother and father, and the interaction between parents and their child.

Expected impact: Our target group is hard to reach, is often burdened by multiple risk factors (e.g. psychological issues), and has the highest risk of unhealthy weight gain in pregnancy and postpartum period. Also, their children have the highest risk of becoming overweight or obese. Therefore, in this group most health benefits can be gained, and developing an intervention strategy specifically designed for this target group is extremely relevant and important. The parents receive support for developing positive parent-child interactions, which will have long-term beneficial effects for the (weight) development of their children. The study adds knowledge on health development, acceptance and impact of mHealth prevention strategies in our target population. To evaluate the interventions in two different countries, with different health care systems, will provide essential information on the effectiveness in different contexts, which is important for further improvement of the interventions.