ABSTRACT
Sex ratio is referred to male, female ratio which is usually 1.06. This ratio is decreased during the last few years. One of it's reasons seems to be poisons and environmental pollutions such as cigarette smoke. In this investigation we studied the relationship between father's cigarette smoking and sex ratio in children.This is a historical cohort study. Study population were neonates born in Arak hospitals during summer and autumn 1383. Sample size was determined 710 neonates, based on alpha = 5%, beta = 10%. Sampling method was census in which all newborns with inclusion criteria were selected and questionnaires were filled. Samples were divided into three groups. 1- Newborns with nonsmoker fathers 2- Newborns with smoker fathers [less than 20 cigarettes a day] 3- Newborns with smoker fathers [20 or more cigarettes a day][Father's cigarette smoking at least 3 months before conception in second and third group]. Newborn's sex ratio was determined in each group and caparisoned. Data analysis was done by frequency, ratio, mean and standard deviation indexes and K-S, leven, t, mann-whitney, chi square tests and relative risk, using SPSS software. At all stages of the study Helsinki declaration was regarded.Overall sex ratio was 1.04. This ratio was 1.272 for neonates with nonsmoker fathers and 0.77 for neonates with smoker fathers. Also sex ratio in newborns with smoker fathers using less than 20 cigarettes a day was 0.846 and for those with fathers using 20 or more was 0.60. Based on chi square there was a meaningful relationship between the three groups[p<0.00001]. Relative risk in low cigarette group was 1.23 and in high cigarette group 1.42.Based on findings it seems that father's cigarette smoking near conception results in decreasing sex ratio and the increased use of cigarettes the decreased born of male neonates