Babies with low birth weight, small for gestational age (SGA) and large for gestational age (LGA) are at increased risk of many perinatal complications.To evaluate the risks factors associated with SGA and LGA births at Buriram Hospital.Pregnant women who were admitted to the labor room at Buriram hospital were selected, alternate cases in the daytime between October 2012 and January 2013. Pre-pregnancy BMI and gestational weight gain were categorized based on Institute of Medicine BMI groups. The predicted risk of either SGA or LGA births were estimated using generalized linear modeling and multivariate regression.Data were collected on 197 pregnant women including pregnancy characteristics, antenatal care, labor characteristics, maternal complications and neonatal health. The average maternal age was 25.74 ± 6.47 years old. The results showed that the factors of weight gain during pregnancy < recommend for the pre-pregnancy BMI weight, gestational age < 37 weeks and pregnancy induce hypertension were correlated with SGA by logistic regression. Maternal age < 19 years old was correlated with a lower incidence of LGA. When using multivariate analysis the factor associated with SGA was gestational age < 37 weeks (Adjusted odds ratio 10.403, 95% CI 2.109-51.313, p = 0.004), whereas the factor associated with decreased LGA was maternal age < 19 years old (Adjusted odds ratio 0.128, 95% CI 0.017-0.983, p = 0.048).The risk factor associated with SGA was gestational age < 37 weeks. The factor associated with LGA was maternal age, with maternal age < 19 years old having the least incidence for LGA. Public health programs should be targeted towards improving antenatal care screening and close monitoring including maternal age, gestational weight gain, monitoring obstetric care, prevent preterm delivery and providing proper newborn resuscitation in order to decrease perinatal complications and improve the quality of perinatal health.