Objectives: Our main objective was to assess sociodemographic differences in the probability of prenatal diagnosis of congenital heart defects (CHD); we also looked at differences in termination of pregnancy for fetal anomaly (TOPFA). Design: Prospective cohort observational study. Setting: Population-based cohort of CHD (live births, TOPFA, fetal deaths) born to women residing in the Greater Paris area (Paris and its surrounding suburbs, N=317 538 total births). Participants: 2867 cases of CHD, including 2348 (82%) live births, 466 (16%) TOPFA and 53 (2%) fetal deaths. Primary and secondary outcome measures: Differences in the probability of prenatal diagnosis by maternal occupation, geographic origin and place of residence; differences in the probability of TOPFA. Results: 29.1% (95% CI 27.5% to 30.8%) of all CHD were prenatally diagnosed. Probability of prenatal diagnosis was similar by maternal occupation, geographic origin and place of residence. In contrast, there were substantial differences in the probability of TOPFA by maternal geographic origin; differences by maternal occupation and place of residence were generally smaller and not statistically significant. Conclusions: Our findings suggest that an appropriate health system organisation aimed at providing universal, reimbursed specialised services to all women can provide comparable access to prenatal diagnosis for all sociodemographic groups. In contrast, we found substantial differences in TOPFA for women of different geographic origins, which may reflect women's preferences that should be respected, but that can nonetheless lead to the situation where families with fewer resources will be disproportionately responsible for care of newborns with more severe forms of CHD.