A retrospective study was carried out by reviewing 5200 medical records of pregnant women who delivered at the Department of Obstetrics and Gynecology, Faculty of Medicine Siriraj Hospital during 1 September 2011–1 August 2012. Inclusion criteria were singleton pregnancy with available prepregnant weight and maternal height. Pre-pregnancy BMI were categorized according to World HealthOrganization criteria. Pregnancy outcomes of interest were appropriate for gestational-age infants. The optimal gestational weight gain for each BMI group was proposed to achieve a high proportion of appropriate for gestational age infants.