RESUMO
The prevalence of low birth weight is one of the important sanitary indices in evaluating the prenatal care all over the world. So, recognition of risky factor to low birth weight can help prevent the occurrence of being low birth weight. To determine the prevalence of low birth weight in Guilan and comparison of many biological characteristics of mothers of low birth weight babies with those of the mothers with normal weight babies. In the descriptive- analytical study, first, all newborn babies in 20 hospitals and maternity centers between Day [Jan. 2008] and Azar [Nov. 2009] were selected. Then, 168 low birth weight babies and 157 normal weight babies were randomly selected along with their mothers who filled the biological characteristics questionnaire with 0/85 validity. Variables in this research includes the condition of mother's nourishment, smoking, suitable mobility and rest, high blood pressure, exposure to X-ray, and bleeding during pregnancy. Since the variables were classical, [nominal scale], the data were analyzed by qui statistical method and Phi coefficient in meaningful level [p