Background: Lifestyle behaviors during the periconception period contribute to achievement of a successful pregnancy. Assessment of attitudes and practices toward these modifiable behaviors can aid in identifying gaps in unhealthy lifestyle behaviors with impact on intervention effectiveness. Objective: This study investigates the effectiveness of coaching by the eHealth program Smarter Pregnancy during the periconception period on improvement of attitudes and practices toward fruit and vegetable intake and smoking in women attempting pregnancy through assisted reproductive technology (ART) or natural conception. Methods: Women attempting pregnancy through ART (n=1060) or natural conception (n=631) were selected during the periconception period. The intervention groups, conceived through ART or naturally, received Smarter Pregnancy coaching for 24 weeks, whereas the control group conceived through ART and did not receive coaching. Attitudes and practices at baseline and follow-up periods were obtained from self-administered online questionnaire provided by the program. Attitudes were assessed in women with unhealthy behaviors as their intention to increase their fruit and vegetable intake and to quit smoking using a yes/no question. Outcomes on practices, suggesting effectiveness, included daily fruit (pieces) and vegetable (grams) intake, and if women smoked (yes/no). Changes in attitudes and practices were compared at 12 and 24 weeks with baseline between the ART intervention and ART control groups, and within the intervention groups between ART and natural conception. Changes in practices at 12 and 24 weeks were also compared with baseline between women with negative attitude and positive attitude within the intervention groups: ART and natural conception. Analysis was performed using linear and logistic regression models adjusted for maternal confounders and baseline attitudes and practices. Results: The ART intervention group showed higher vegetable intake and lower odds for negative attitudes toward vegetable intake after 12 weeks (βadj=25.72 g, P<.001; adjusted odds ratio [ORadj] 0.24, P<.001) and 24 weeks of coaching (βadj=23.84 g, P<.001; ORadj 0.28, P<.001) compared with ART controls. No statistically significant effect was observed on attitudes and practices toward fruit intake (12 weeks: P=.16 and .08, respectively; 24 weeks: P=.16 and .08, respectively) and smoking behavior (12 weeks: P=.87; 24 weeks: P=.92). No difference was observed for the studied attitudes and practices between the ART intervention and natural conception intervention groups. Women with persistent negative attitude toward fruit and vegetable intake at week 12 showed lower fruit and vegetable intake at week 24 compared with women with positive attitude (βadj=–.49, P<.001; βadj=–30.07, P<.001, respectively). Conclusions: The eHealth Smarter Pregnancy program may improve vegetable intake–related attitudes and practices in women undergoing ART treatment. Women with no intention to increase fruit and vegetable intake had less improvement in their intakes. Despite small changes, this study demonstrates again that Smarter Pregnancy can be used to improve vegetable intake, which can complemented by blended care that combines face-to-face and online care to also improve fruit intake and smoking behavior.