Objective: To evaluate gestational weight gain (according to the Institute of Medicine recommendation) and pregnancy outcomes by comparing the Western and Asia-Pacific Pre-pregnancy Body Mass Index. Design: A retrospective study. Setting: Maternal and Child Health Clinics in Brunei. Population or Sample: Health medical records of mothers. Methods: Demographic factors, pre-pregnancy Body Mass Index, gestational weight gain, and maternal and neonatal outcomes were retrieved. Univariate analyses were applied. Main outcome measures: Maternal and neonatal outcomes. Results: 170 records were extracted. Adverse neonatal outcomes (p=0.036) were detected when gestational weight gain was evaluated using the Asia-Pacific pre-pregnancy Body Mass Index as compared to that of the Western (p=0.440). The prevalence of obese women was significantly higher (95%CI: 36.0, 51.3) compared to (95%CI: 11.4, 23.1)(p<0.001). The gestational weight gain above the recommended guideline was also significantly higher (95%CI: 71.1, 84.0) compared to (95%CI: 60.6, 75.0) (p<0.001). Conclusions: Evaluating gestational weight gain using the Asia-Pacific pre-pregnancy Body Mass Index and the Institute of Medicine guidelines was significant in detecting adverse neonatal outcomes and prevalence of obesity in the Asian pregnant women population in Brunei. This retrospective study served as a platform for more rigorous study on larger population.