OBJECTIVE: To compare the perinatal outcomes of women with Gestational Diabetes Mellitus (GDM), between pregnant treated only with lifestyle changes and pregnant treated with insulin and lifestyle changes. METHODS: Prospective cohort study with follow-up of 64 women with GDM during the prenatal care and postpartum period until hospital discharge, divided into a control group (43) and an insulin group (21), with collection of sociodemographic, clinical, glycemic control and perinatal outcome data. Fetal macrosomia (≥ 4 Kg), or large-for-gestational-age newborns were considered the primary outcome of the research. RESULTS: Pre-pregnancy BMI (31.2 ± 3.9 versus 28.8 ± 5.5), diastolic blood pressure (75 ± 8.7 versus 69 ± 6.9) and postprandial blood glucose (136.6 versus 115.4) were higher in the insulin group, respectively. The control group had an average birth weight of 3058 g and an incidence of preterm birth of 11.6 %, while the insulin group had an average birth weight of 3203 g, with an incidence of preterm birth of 4.8 %. The majority of newborns had an adequate weight for their gestational age. Even all participants met glycemic goals, in the insulin group the Apgar score at the 5th minute and exclusive breastfeeding was lower, had 100 % of resuscitation cases, and a longer inpatient period. CONCLUSION: These data reinforce that even during prenatal care with lifestyle changes, newborns of women with GDM treated with insulin had worse outcomes, including clinical complications and less exclusive breastfeeding. It is important in prenatal care to identify neonates with risk for prevention and health promotion measures.