The aim of this study was to estimate standards of large-for-gestational-age (LGA) infants of twin pregnancies based on the incidence of neonatal hypoglycemia. We examined 277 dichorionic twin infants (in 201 dichorionic twin pregnancies) who were delivered weighing > or = 2,500 g at 37-41 weeks of gestation. LGA in twin pregnancies was identified when the infant deviated > by 1.5SD from the mean gestational age of this study (LGA based on the twin pregnancy standard), or when the infant deviated by >1.5 SD of the intrauterine growth curve of Japanese (LGA based the singleton pregnancy standard). Using the twin pregnancy standard, the incidence of neonatal hypoglycemia in LGA twin infants was not measurably different from that in appropriate-for-gestational-age (AGA). However, using the singleton pregnancy standard, the incidence of neonatal hypoglycemia was significantly higher than that in AGA infants. In conclusion, LGA in twin pregnancies should be studied based on the singleton pregnancy standard to assess the incidence of neonatal hypoglycemia.