Study objective: The aims were (1) to assess whether termination of pregnancy after prenatal screening by ultrasound affected the prevalence of congenital anomalies at birth, and (2) to examine the trend of this pattern over time.

Design: This study deals with congenital anomalies, possibly detectable prenatally or at birth, which were classified as isolated and multiple anomalies; chromosomal anomalies were not included. The prevalence rates of congenital anomalies at birth were determined from case registration data in the Marseille district, France, from the registry of congenital malformations (Eurocat no 22), which covers 23,500 births a year. The chi 2 test for homogeneity in proportions was used to test whether the differences in the total prevalence rates were significant over time.

Setting: The population was defined as all children born to parents living in the Marseille district between January 1 1984 and December 31 1990.

Patients: Among the 164,509 pregnancy outcomes monitored during the study, 1795 children with a single congenital anomaly and 288 with multiple congenital anomalies detectable at birth were assessed.

Measurements and main results: The percentage of pregnancy terminations was higher in the case of multiple anomalies (16%) than with single ones (7.5%). Leaving aside the lethal birth defects, this percentage became 7.9% in the case of multiple anomalies and 4.3% with isolated ones. A significant increase (p < 0.001) occurred over the seven year study period in the total percentage of terminations because of isolated anomalies but not in that involving multiple ones. The increase observed in the former case was found to be mainly attributable to an increase in the number of terminations of pregnancy undertaken because of anomalies which were either lethal or associated with very low survival rates (p < 0.001).

Conclusions: Termination of pregnancy after prenatal ultrasound examination was found to have a definite impact on the prevalence at birth of lethal and congenital anomalies with a low survival rate, and this impact tended to increase over time. No such impact was observed in the case of congenital anomalies associated with high survival rates.