Aim: The authors determined the impact of antenatal counseling against exposure to environmental cigarette smoke on the prevention of reduced neonatal birth weight according to gestational age. Materials and Methods: A cross-sectional study was conducted in pregnant women, with 77 passive smokers and 88 non-smokers. During motivational interviews, passive smoking status was monitored and additional follow-up visits were arranged to increase the knowledge regarding perinatal risks of passive smoking, including intrauterine growth restriction and low birth weight. The authors aimed to increase the woman’s motivation to avoid second-hand tobacco smoke exposure. Results: The demographic and clinical findings of the study groups were found considerably similar, in this context, and the authors found positive and strong correlations between the gestational age and neonatal birth weight (r = 0.80 and r = 0.76, respectively; p < 0.05). Conclusions: During antenatal care of women, regular counseling against second-hand smoke exposure may prevent negative effect of passive smoking on neonatal birth weight according to gestational age. This promising finding needs to be supported by further studies with larger sample size considering covariates relevant to passive smoking.