Introduction: Earlier studies throughout the world show that the ratio of live male births to live female births is declining. There are several factors associated with the reduction of male births including environmental pollutions, exposure to chemicals and smoking. The aim of this study is to determine the relationship between paternal smoking and sex ratio of children at public maternity hospitals in Bandar Abbas. Methods: The present cross-sectional study surveyed public hospitals in Bandar Abbas (Iran) from 21 March 2010 to 20 March 2011. Data was collected by census method. Seven hundred thirty mothers eligible for the completed a questionnaire and provided required information. Then sex ratio was compared in two groups. Three hundred sixty five mothers lived with smoker spouse and 365 did not. Data analysis was done by SPSS statistical software using descriptive methods, Chi-square test and logistic regression analysis. Results: Results showed that the spouses with lower education smoked cigarettes more than those with higher education. The difference was statistically significant (P<0.0001). Sex ratio for children with smoker father and the group with non-smoker father was 0.7 and 1.2, respectively; and the relationship was significant (P<0.001). Out of 365 smoker fathers, 283 cases smoked less than 20 cigarettes per day, and 82 smoked more than 20 cigarettes. The sex ratios for the babies with smoker fathers smoking less than 20 cigarettes and those smoking more than 20 cigarettes were 0.76 and 0.56, respectively. Conclusion: Based on the study, it seems that smoking cigarette by parents during conception period may have a negative effect on the sex ratio. Therefore, the gender of the fetus tends to be female.

Keywords: Sex Ratio, Smoking, Sex

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