Background : Substance use during pregnancy is greatly underestimated in many parts of the world. Specifically, there are limited up-to-date researches addressing the relationship between substance use and birth outcomes among women in Ethiopia. Therefore, having a study to close the gap and generate firsthand information on the issue is important. The aim of this study is to determine the effect of maternal substance use during pregnancy on the birth weight of a newborn. Methods : The study used analytic facility based case control study, using a face to face interview with a structured and pre-tested questionnaire. The total sample size was allocated to each health facility based on their patient load through proportion to population size, and a total of 112 cases of neonates with low birth weight (weight < 2500gms) were compared with 235 controls of neonates, born with a birth weight above 2500 grams or more. The data were analyzed using both bivariate and multivariable analysis. Results : - Maternal khat chewing, tobacco smoking and narghile (shisha) smoking during pregnancy and paternal smoking were statistically associated with lower birth weight. However, maternal history of alcohol drinking during pregnancy was not associated with lower birth weight. Mothers who did not attend primary school and having history of previous low birth weight child were statistically associated with low birth weight. Moreover, lesser weight gains during pregnancy and short intra pregnancy interval were associated with low birth weight. Conclusion : - The association of low birth weight with substance use was strong, particularly, with maternal khat chewing, cigarette and narghile (shisha) smoking including passive smoking during pregnancy. Therefore, we recommend health professionals working in antenatal care service, be aware, on counseling of mothers for banning or lowering use of substance during pregnancy.

Key word: Substance use, Pregnancy, Birth weight, Smoking, Khat chewing, Ethiopia