Objective To assess the prevalence, timing of diagnosis and infant mortality of congenital heart defects (CHD) with population-based data and using a classification that allows regrouping of the International Paediatric and Congenital Cardiac Code into a manageable number of categories based on anatomic and clinical criteria (ACC-CHD).

Design Population-based cohort study.

Setting Greater Paris.

Patients All cases (live births, terminations of pregnancy for foetal anomaly (TOPFA), foetal deaths) diagnosed prenatally, or up to 1 year of age in the birth cohorts, May 2005–April 2008, for women in Greater Paris (n=317 538 births). Diagnoses were confirmed in specialised centres and subsequently coded and classified into the categories of ACC-CHD by paediatric cardiologists in the study group.

Results The total number of CHD was 2867, including 2348 live births (82%), 466 TOPFA (16.2%) and 53 foetal deaths (1.8%). The total prevalence of CHD was 90 per 10 000. After exclusion of ventricular septal defects (VSD), 40% of ‘isolated’ CHD was diagnosed prenatally with about one half of the remaining diagnosed before 7 days of age. Nevertheless, one in five cases of these major CHD was diagnosed after the fourth week. Infant mortality of ‘isolated’ CHD-VSD excluded was 8.5% with 40% of deaths occurring after the fourth week of life. These outcomes varied substantially across categories of ACC-CHD.

Conclusions Timing of diagnosis, TOPFA, risk and timing of infant mortality were highly variable across the categories of CHD in ACC-CHD, suggesting that it may be a useful measure of severity, and hence, predictor of outcomes of CHD.