Objective: A population-based study of the trends in accuracy over time of prenatal diagnosis of congenital malformations.
Design: A prospective study of all congenital malformations.
Setting: The counties of Cleveland, Durham, North Cumbria, Northumberland and Tyne and Wear.
Population: All 573,471 babies born to residents at 24 weeks of gestation or more, and all terminations for fetal abnormality, occurring between 1985 and 2000.
Methods: An analysis of all congenital anomalies whether antenatally detected or diagnosed before one year of age to examine the accuracy of prenatal diagnosis and its trends over four consecutive four-year periods.
Main outcome measures: The proportion of cases where a diagnosis before birth was correctly made, wrongly made or not made in a range of important structural malformations.
Results: There was a substantial improvement in the accuracy of prenatal diagnosis of all conditions reported here. However, the extent to which different conditions were diagnosed varied widely. It now exceeds 90% for anencephaly and for abdominal wall defects but is still less than 70% for diaphragmatic hernia, bladder outlet obstruction and many major skeletal defects. Termination of pregnancy for fetal malformation rose from 23 to 47 per 10,000 registrable births.
Conclusion: This large prospective study provides data on the accuracy of prenatal diagnosis of a number of malformations in a geographically defined population under service conditions. Diagnostic accuracy has improved over time but may well be lower than many clinicians assume for some important conditions and may not match public expectations.