Background: Pregnancy during adolescence is a prevalent condition in low and middle-income countries (LMIC) associated with various adverse outcomes. However, testing early childhood development interventions in LMIC can be challenging due to limited resources. The use of ambulatory assessment (AA) delivered via smartphone can be an alternative data collection method ideal to measure outcomes in an environment with adverse conditions. Objective: Our study had two objectives. First, to investigate the adequacy of an eDiary protocol to measure daily maternal care experience of participants. Second, to test the efficacy of a nurse home visiting intervention on child maternal care and parental well-being. Methods: We conducted a randomized controlled trial to test the efficacy of Primeiros Laços, a nurse home visiting program for adolescent mothers living in an urban deprived area of São Paulo, Brazil. One hundred and sixty-nine pregnant youth were assessed for eligibility criteria and 80 youth were included and randomized to intervention (n=40), and control group (care as usual, n=40). Primeiros Laços is a home visiting intervention delivered by trained nurses tailored to first-time pregnant adolescents and their children, starting during the first 16 weeks of pregnancy to the child’s 24 months. Participants were assessed by blind interviewers at 8-16 weeks of pregnancy (baseline), 30 weeks of pregnancy, 3, 6, and 12 months of child’s age. At 18 months participants were assessed regarding maternal care and parental well-being using a 7 consecutive days electronic daily diary (eDiary). The smartphone app was programmed to notify participants every day at 9:00 p.m. over a period of seven days. Results: We were able to contact 57 (71.3%) participants (29 intervention, 28 control) at 18 months of the child’s age. Forty-eight (84.2%) participants responded at least one day of the eDiary protocol. Our analyses showed the effect of the intervention on parental well-being (B=0.32, P=.015) and mother telling a story or singing to the child (OR=2.33, P=.012). Conclusions: eDiary was accepted by adolescent mothers living in an urban deprived area as a method of assessment. Our findings showed the efficacy of Primeiros Laços on improving maternal child care and parental well-being. Primeiros Laços is a promising intervention to promote maternal child care and well-being among low income adolescent mothers. Future studies can implement AA in LMIC via smartphones to measure mother and child behaviors. More frequent assessments should be implemented to further enhance temporal and ecological validity, and also to increase the scope of measured behaviors. Clinical Trial: Trial registration at clinicaltrial.gov: NCT02807818.
