The identification of gestational diabetes (GDM) through appropriate screening and its subsequent treatment have not been demonstrated to limit neonatal malformations to date. This study aimed to detect congenital heart diseases in newborns of mothers with GDM by evaluating the existence of a correlation with maternal glycemic control. This observational prospective study investigated newborns of mothers with GDM enrolled during a period of 9 months. Four subgroups were considered according to the type of maternal glucidic alteration during pregnancy and the home treatment: impaired glucose tolerance, insulin-dependent gestational diabetes mellitus (IDDM), non-insulin-dependent gestational diabetes mellitus (NIDDM), and gestational diabetes not controlled (NC: untreated diabetes). Student’s t test was used to compare the subgroups. The study enrolled 65 newborns (30 boys) born to 82 of mothers with impaired glucidic metabolism. Patent ductus arteriosus was observed in 11 patients (16.9 %), pulmonary stenosis of mild grade in 4 patients ( 6.2 %), and hypertrophy of the ventricular septum in 22 patients (33.8 %). A total of 14 patients had increased thickness in the left ventricle posterior wall, and 17 patients had an abnormal electrocardiogram. Hyperglycemia can influence the development of the fetal heart, affecting both its structure and its function. A treatment with insulin for women with GDM is supported by the study data.