Prenatal diagnosis and prevalence of Down syndrome in the Parisian population, 2001-2005

OBJECTIVES: To assess recent trends in the prevalence of Down syndrome and the proportion of cases with a prenatal diagnosis in the Parisian population. PATIENTS AND METHODS: Four hundred and ninety-nine cases of Down syndrome were registered by the Paris Registry of Congenital Anomalies during the period 2001-2005. All cases with prenatal diagnosis were confirmed by cytogenetic examination. We analyzed trends in the total and live birth prevalence, the proportion of cases with a prenatal diagnosis and those with a pregnancy termination, as well as gestational age at diagnosis and termination. Analyses were stratified by maternal age and trends were tested by the Cochran-Armitage test and Anova. RESULTS: Total prevalence of Down syndrome remained high (37.6 per 10,000 births, 95%CI 34.2-40.9) during this period because of advanced maternal age in Paris. The proportion of cases with a prenatal diagnosis (overall average 85.5%, 95% CI 81.8-88.1), and live birth prevalence of Down syndrome (7.1 per 10,000 live births, 95%CI 5.7-8.6) have remained fairly stable over time. The great majority of women (95% CI 95% 92.7-96.9) opted for a pregnancy termination following a prenatal diagnosis of Down syndrome. A trend towards an earlier gestational age at prenatal diagnosis was noted among women less than 30 years of age. DISCUSSION AND CONCLUSION: It is important to continue to evaluate changes in the prenatal diagnosis of Down syndrome, notably in view of potential changes in screening practices and policies, and particularly if a first trimester strategy is adopted following recent recommendation by the "Haute Autorité de santé".