The relationship between zinc and infant birth weight is still contradictory and up until today there is still no research on this issue done in Iran. This unmatched case control study to evaluate the association between plasma cord blood zinc and infant birth weight at the time of delivery was carried out in the labor ward, Fatemieh Hospital, Hamadan, Iran from the 6 th December 2009 to 18 October 2010. Plasma venous cord blood zinc was measured by AtomicAbsorption Spectro-photometry (AAS) and the weight of 134 Low Birth Weight (LBW) infants (cases) and 134 normal
weight infants (control) were measured at the time of delivery. All mothers with history of chronic diseases, obstetric complications, anemia, twin pregnancy, smoking, using illicit drugs, and alcohol and infants with any obvious anomalies were excluded from this study. Data were analyzed using SPSS version 16. Logistic regression was used to assess the contribution of other risk factors on infant birth weight. The result showed there was significant relationship between infant birth weight and plasma cord blood zinc. The risk of having LBW infant is more than 12 times in mothers who have severe zinc deficiency (OR=12.234,CI 95% 1.122, 133.392, p-value= 0.040). Also in mothers
who have mild to moderate zinc deficiency the risk of having LBW was more than one (OR=1.148, CI 95% 0.358, 3.900, p-value= 0.797). A significant relationship between maternal pre-pregnancy Body Mass Index (BMI) (p< 0.002), maternal weight gain during pregnancy (p< 0.021), previous LBW (p< 0.016), maternal age (p< 0.034) and parity (p< 0.004) with infant birth weight were also found. Logistic regression showed that zinc deficiency along with maternal pre-pregnancy BMI, maternal weight gain during pregnancy, previous LBW, maternal age and parity were predictors
for infant birth weight.