Objective Congenital heart disease (CHD) is the most common congenital malformation and causes major morbidity and mortality. Prenatal detection improves the neonatal condition before surgery, resulting in less morbidity and mortality. In the Netherlands a national prenatal screening programme was introduced in 2007. This study evaluates the effects of this screening programme. Design Geographical cohort study. Setting Large referral region of three tertiary care centres. Population Fetuses and infants diagnosed with severe CHD born between 1 January 2002 and 1 January 2012. Methods Cases were divided into two groups: before and after the introduction of screening. Main outcome measures Detection rates were calculated. Results The prenatal detection rate (n = 1912) increased with 23.9% (95% confidence interval [95% CI] 19.5–28.3) from 35.8 to 59.7% after the introduction of screening and of isolated CHD with 21.4% (95% CI 16.0–26.8) from 22.8 to 44.2%. The highest detection rates were found in the hypoplastic left heart syndrome, other univentricular defects and complex defects with atrial isomerism (>93%). Since the introduction of screening, the ‘late’ referrals (after 24 weeks of gestation) decreased by 24.3% (95% CI 19.3–29.3). Conclusions This is the largest cohort study to investigate the prenatal detection rate of severe CHD in an unselected population. A nationally organised screening has resulted in a remarkably high detection rate of CHD (59.7%) compared with earlier literature.