Iranian Red Crescent Medical Journal Maternal and Prenatal Risk Factors for Childhood Leukemia in Southern of Iran J Hassanzadeh 1 , R Mohammadi1, AR Rajaeefard 1 , MR Bordbar2*, M Karimi2 1Department of Epidemiology, School of Health and Nutrition, Shiraz University of Medical Sciences, Shiraz, Iran; 2Hematology Research Center, Shiraz University of Medical Sciences, Shiraz, Iran ORIGINAL ARTICLE Abstract Background: The causes of childhood leukemia as the most common malignancy in children are vastly un- known. The aim of this study is to evaluate the relationship between maternal birth characteristics with environ- mental exposures in childhood leukemia. Methods: This is a case-control study which consists of children younger than 18 years old suffering from leu- kemia who reside at Fars Province of Iran. Patients were individually matched with variables such as age, sex and residence region. In order to evaluate the relationships between each variable and the risk of leukemia, odds ratio(OR) and 95% confidence interval (CI) were estimated using conditional logistic regression. Results: Statistically, the association between risk of childhood leukemia with birth order (OR=6.177, 95%CI: 2.551-14.957), pet ownership (OR=2.565, 95%CI: 1.352-4.868) and history of leukemia in first and second de- gree relatives (OR=2.667, 95%CI: 1.043-6.815) was significant. However, there was no significant association between daycare attendance, history of miscarriage, number of siblings and history of mother's diagnostic radiol- ogy tests with risk of childhood leukemia. Conclusion: Although no definite etiologic factor for acute childhood leukemia has been clearly defined, the contribution of environmental risk factors in the context of genetic predisposition are strongly elucidated. Keywords: Leukemia; Children; Risk factors; Prenatal; Genetics Introduction Leukemia is the most common type of childhood ma- lignancy which accounts for approximately 30% of cancer cases in children younger than 15 years old.1-3 It is the primary cause of childhood cancer mortality in the United States and approximately 6000 new cases are diagnosed each year.4 The etiology of child- hood leukemia is mostly unknown. Epidemiologic studies have examined a number of possible risk fac- tors including environmental, genetic and infectious causes. Links between most environmental risk fac- tors (eg. electromagnetic fields, cigarette smoking) *Correspondence: Mohammad Reza Bordbar, MD, Hematology Research Center, Nemazee Hospital, Shiraz University of Medical Sciences, Po Box: 71937-11351, Shiraz, Iran. Tel/Fax: +98-711- 6473239, e-mail: bordbarm@sums.ac.ir Received: November 12, 2010 Accepted: January 10, 2011 and childhood leukemia are inconsistent. However, researches present conclusive link between ionizing radiation and leukemia.2,5 Certain inherited diseases like fanconi anemia, bloom syndrome, ataxia telangiectasia, Schwachman syn- drome and neurofibromatosis are associated with a higher risk of developing leukemia.2 An identical twin is twice as likely as the general population to develop leukemia if the illness diagnosed before the age of 7 years.6 Constitutional factors such as male gender, white race and high birth weight have been reported to increase the risk of leukemia.7,8 The infectious etiology hypothesis for childhood leukemia may be supported by socioeconomic and sea- sonal variations in the incidence of childhood leukemia as well as the clustering of leukemia cases.9,10 Several indirect markers of exposure to infectious agents in- cluding birth order, daycare attendance and low socio- economic class have been associated with leukemia. Iran Red Crescent Med J 2011; 13(6):398-403 ©Iranian Red Crescent Medical Journal