IMPORTANCE The occurrence of major congenital heart disease (CHD) is affected by several variables. Determining the development of the true incidence is critical to the establishment of proper treatment of these patients. OBJECTIVE To evaluate time trends in incidence, detection rate, and termination of pregnancy (TOP) rate of major CHD in fetuses in Denmark and assess the influence of the introduction of general prenatal screening in 2004. DESIGN, SETTING, AND PARTICIPANTS Nationwide, population-based, retrospective observational study in Denmark from 1996 to 2013 that included a consecutive sample of 14 688 live-born children and terminated fetuses diagnosed as having CHD. Patient records on TOP and children with major CHD were reviewed to validate the diagnoses. Major CHD included univentricular heart, transposition of the great arteries, congenitally corrected transposition of the great arteries, truncus arteriosus, interrupted aortic arch, atrioventricular septal defects, double outlet right ventricle, coarctatio of the aorta, Ebstein anomaly, pulmonary atresia with ventricular septal defect, pulmonary atresia with intact ventricular septum, and tetralogy of Fallot. Data were analyzed between January 2017 and March 2018. MAIN OUTCOMES AND MEASURES Temporal changes in incidence, detection rate, and TOP of major CHD. RESULTS Of 14 688 children and fetuses diagnosed with CHD, 2695 (18.4%; 95%CI, 17.8-19.1) had major CHD. A total of 7131 boys (1304 with major CHD) and 6926 girls (920 with major CHD) were included, with a median age of 11 years (interquartile range, 6-15 years). During the study period, the live-birth incidence of CHD was constant at 1.22%(95%CI, 1.18-1.26), whereas it decreased for major CHD. When including TOP, the incidence of major CHD did not change over time. The detection rate of major CHD increased from 4.5%(95%CI, 1.2-7.8) to 71.0%(95%CI, 63.3-78.7) (P < .001). At the end of the study, all cases of double outlet right ventricle, Ebstein anomaly, congenitally corrected transposition of the great arteries, and pulmonary atresia with ventricular septal defect were detected prenatally, whereas coarctation of the aorta had the lowest detection rate (21.7%; 95%CI, 3.5-40.0). The TOP rate increased from 0.6%(95%CI, -0.6 to 1.9) to 39.1%(95%CI, 30.9-47.4) (P < .001) among all major CHD. For prenatally diagnosed major CHD, 57.8%of cases were terminated and the proportion did not change significantly throughout the study. Diagnoses leading to TOP included all major CHD diagnoses. CONCLUSIONS AND RELEVANCE Detection rates of major CHD improved during the study. This has led to increased TOP rates, with a subsequent 39%decrease in the live-birth incidence of major CHD.