Background & Aim: It is important to identify modifiable causes of preterm delivery and low birth weight; which are strong predictors of infants' later health status and survival. Research findings show that there are less low birth weight and preterm labors in the communities that have high intake of sea food. Consumption of Sea foods rich in w3 fatty acid can increase birth weight by prolonging gestation and reduce the risk of occurrence of preterm delivery.

Methods & Materials: In this prospective cohort study, samples (n=1200) were selected among pregnant women with different pattern of seafood intake at 16^th week of pregnancy receiving routine antenatal care in Gilan prenatal clinics. Subjects were selected by random sampling method. Women who had risk factors for preterm delivery or fish allergy were excluded. During 2004-2005 the pregnant women were visited monthly to determine their dietary habits (seafood intake). Infants' weight and mothers' gestational age were determined at the time of delivery. Data were collected by means of a validated self-determined questionnaire and a check- list.  Statistical analysis was carried out using SPSS statistical software package.

Results: Results showed that the per cent of term delivery (more than 37 gestational weeks) in women with more than 3 times, 1-3 times, and less than once sea food intake in a day is respectively 94.5%, 91%, and 91.5%. Moreover, birth weights more than 3000 gram in the neonates of these women were respectively 75.7%, 74.7%, and 71.2%. There was significant relationship between more than 3 times consumption of sea food in a month with gestational age (P<0.001) and birth weight (P<0.05).

Conclusion: Sea food consumption is effective in decreasing preterm delivery and low birth weight. Related nutritional educational programs for pregnant women are recommended.