Analytical plan. The required sample (100 intervention vs. 100 control at final follow-up) was calculated assuming abstinence rates of 0.3-0.4 (70% or 60% relapse) in the control group compared to anticipated 0.5-0.6 in intervention group, in order to attain 80% statistical power to detect the difference in two-tailed comparisons, alpha 0.05. Beginning with 125 couples in the intervention vs. 125 in the control group at enrollment, consistent with prior projects in Romania, 20% attrition is assumed by the final follow-up at 6 months after birth (100 vs. 100). To evaluate the effectiveness of the intervention, initially unadjusted comparisons of the outcomes in intervention vs. the control groups will be performed. Regression analyses will be used to adjust for group dissimilarities when differences have p-values less than 0.10. A cost-benefit analysis of the intervention will also be performed. The intervention costs will be compared to the health benefits derived from increased mother abstinence rates, increased father quit rates, and reduced family exposure to tobacco smoke. The health benefits will be monetized using estimates available in the research literature. In addition, economic analyses will be presented for various scenarios in which the proposed intervention can be integrated and sustained in the existing Romanian health system.