This study investigated the association between maternal diabetes and overweight or obesity with congenital heart defects (CHDs) in offspring. The research was conducted using a nationwide, population-based register study in Finland, including all children born between 2006 and 2016 (620,751 individuals) and their mothers. The study found that maternal type 1 diabetes (T1D) was associated with a 3.77-fold increased risk of any CHD in offspring, with increased risk in 6 of 9 CHD subgroups. Maternal overweight was associated with left ventricular outflow tract obstruction and ventricular septal defects, while maternal obesity was associated with complex defects and right outflow tract obstruction. These findings suggest distinct underlying teratogenic mechanisms for T1D and overweight/obesity. The study also found that maternal overweight was associated with lower odds of ventricular septal defects in offspring. The results indicate that maternal T1D is a significant risk factor for most types of CHD, while maternal overweight and obesity are associated with specific types of CHD. The study highlights the importance of understanding the different risk profiles of T1D and overweight/obesity in relation to CHD. The study also found that the prevalence of maternal diabetes and obesity increased over the study period. The study concluded that maternal T1D is a risk factor for CHD, while maternal overweight and obesity are associated with a smaller increase in risk. The study emphasizes the need for further research to understand the underlying mechanisms of these associations.This study investigated the association between maternal diabetes and overweight or obesity with congenital heart defects (CHDs) in offspring. The research was conducted using a nationwide, population-based register study in Finland, including all children born between 2006 and 2016 (620,751 individuals) and their mothers. The study found that maternal type 1 diabetes (T1D) was associated with a 3.77-fold increased risk of any CHD in offspring, with increased risk in 6 of 9 CHD subgroups. Maternal overweight was associated with left ventricular outflow tract obstruction and ventricular septal defects, while maternal obesity was associated with complex defects and right outflow tract obstruction. These findings suggest distinct underlying teratogenic mechanisms for T1D and overweight/obesity. The study also found that maternal overweight was associated with lower odds of ventricular septal defects in offspring. The results indicate that maternal T1D is a significant risk factor for most types of CHD, while maternal overweight and obesity are associated with specific types of CHD. The study highlights the importance of understanding the different risk profiles of T1D and overweight/obesity in relation to CHD. The study also found that the prevalence of maternal diabetes and obesity increased over the study period. The study concluded that maternal T1D is a risk factor for CHD, while maternal overweight and obesity are associated with a smaller increase in risk. The study emphasizes the need for further research to understand the underlying mechanisms of these associations.