ABSTRACT
Season of birth is one of the environmental factors that may affect birth weight. The aim of this study was to assess the relationship between seasonal patterns and birth weight in an educational center in Iran, 2010. In this cross sectional study, the check list was used for checking of 3076 women that delivered on vaginal method [NVD]. Exclusion criteria included twin delivery, intrauterine fetal death [IUFD], abortion in current pregnancy and delivery by caesarean. 81.2% women were primiparous and 53.3 percent of newborns were boys. The gestational age of 7.4, and 92.6 percent women was preterm and term, respectivly. Average neonatal birth weight was 3248.18 +/- 458 and women mean age was 25.33 +/- 5.7 years. There was a significant relationship between seasonal changes and the mean birth weight [P= 0.018] as the highest weight was in spring and lowest in summer. The highest average birth weight term was the 21 March to 20 April and the lowest month was the 23 August to 22 September [P = 0.064]. Although birth weight can be different with seasonal changes, the role of other environmental factors should not be ignored.