Background: Previous studies on the relation between birth weight and childhood asthma have had conflicting results. The aim of this study was to examine the effect of birth weight on asthma during the first three years of life.

Materials and Methods: This cohort study was performed on 240 neonates in Kashan city between 2009 and 2013(during a period of four years). Subjects were allocated into two groups of low and normal birth weight and were then observed for having asthma over the next three years. Child’s asthma was evaluated by physical examination and, if possible, by using a peak flow meter.

Results: A total of 80 underweight and 134 normal weight children participated in this study. Twenty-one percent of children with low birth weight and 10.4% of children with normal birth weight were affected by asthma (P=0.03). The mean age of developing asthma was 21.53±7.66 months in the low birth weight group and 27.43±6.54 months in the normal weight group (P=0.03). After adjusting for the effect of confounding variables, a significant relationship was found between birth weight and developing asthma (P=0.04).

Conclusion: The results of the present study reveal that low birth weight can be an independent risk factor for developing asthma during the first three years of life.