Prenatal smoking and stress are associated with adverse health effects for women themselves and are risk factors for adverse outcomes of the child. Effective interventions are needed to support women with smoking cessation and reducing stress. The aims were (1) to test the effectiveness of an 8-week eHealth intervention targeting stress reduction and smoking cessation; (2) to examine whether stress reduction mediated the intervention effect on smoking behavior; (3) to test motivation to quit as a moderator; and (4) to investigate a dose–response effect of program usage.

Pregnant women were included if they were >18 years of age, < 28 weeks pregnant at recruitment, and currently smoking. In total, 156 consenting participants were randomly assigned to the intervention or active control condition. Study outcomes on smoking (yes/no, frequency, and quantity) were collected via online questionnaires at pre-intervention (baseline; t0), post-intervention (8 weeks after t0; t1), and follow up at two weeks (t2) and three months (t3) after birth.

Smoking and stress reduced over the 8-week period in both conditions. The intervention effect on smoking was not mediated by stress reduction. Motivation to quit was found to moderate the intervention effect (smoking frequency and quantity) and a dose–response effect was found for program usage in the intervention for the reduction on smoking frequency and quantity.

Program usage and motivation to quit are important for smoking reduction in pregnant women. Further research is needed to examine how the intervention could be improved to increase treatment effectiveness.