['To assess the immunogenicity of same needle length of hepatitis B vaccine for infants with different birthweights. Previous studies have focused on obese adolescents and adults that have lower titers of antibody response to hepatitis B vaccine. The aim of this study was to compare antibody titers of macrosomic and other neonates for hepatitis B antibody with the same needle length.', '96 healthy infants were vaccinated at birth, 1, and 6 months of age with hepatitis B vaccine, with follow-up to 7 months of age. Cord blood and seventh month hepatitis B antibody titer were repeated. Infants were divided into three groups, according to their birthweight, as macrosomic, appropriate for gestational age and small for gestational age. The same needle with 26 G and 16 mm length was used for all infants.', 'Macrosomic infants with a birthweight over 4000 g had lower antibody levels than small and appropriate for gestational age infants.'] Does response to hepatitis B vaccine differ by birthweight among neonates?