Aims: To evaluate the effects of pre-gestational diabetes mellitus (PGDM) and gestational diabetes mellitus (GDM) on macrosomia and birth defects. Methods: Existing birth registry data from the Perinatal Data System in Upstate New York was analysed. 650,914 women with a singleton term pregnancy (>= 37 weeks) aged 18-55 years from 2004 to 2016 were included. Results: The prevalence of macrosomia in infants born to women with PGDM and GDM were 26.0% and 16.4%, respectively, higher than that in the controls (11.2%). Compared with the controls (0.8%), the PGDM and GDM groups had higher prevalence of any birth defect (1.8% and 1.0%). The PGDM group had the highest prevalence of cyanotic heart disease (0.6%). Moreover, the PGDM group had higher prevalence of cleft lip and palate, cleft palate alone, hypospadias and limb reduction defect compared to the GDM and control groups (p < 0.05). However, these birth defects in the GDM group were similar to those in the controls. Both the PGDM and GDM groups had significantly elevated odds of macrosomia, cyanotic heart disease and any birth defect than controls. The PGDM group had higher odds of cleft lip and palate, cleft palate alone, hypospadias and limb reduction defect. Conclusions: Using the Perinatal Data System database, PGDM and GDM, especially PGDM, was associated with higher prevalence of macrosomia, cyanotic heart disease and any birth defect in singleton term pregnancy in Upstate New York. PGDM, not GDM had higher prevalence of cleft lip and palate, cleft palate alone, hypospadias and limb reduction defect. (C) 2019 Elsevier B.V. All rights reserved.