The evolution of prenatal screening and diagnosis and its impact on an unselected population over an 18-year period

Abstract

Objective: To review changes in and impact of prenatal screening and diagnosis.

Design: Population-based congenital anomaly register study.

Setting: Oxfordshire.

Population: Congenital anomalies confirmed and those suspected prenatally, delivered 1991-2008.

Methods: Analysis of proportions of congenital anomalies confirmed and those suspected prenatally.

Main outcome measures: Birth prevalence, prenatal detection rates, pregnancy outcomes.

Results: A total of 2651 (2.3%) infants/fetuses had a congenital anomaly diagnosed. There were 3839 suspected or confirmed cases, 2847 due to a prenatal suspicion, of which 1659 had an anomaly confirmed at delivery, and 1188 false-positive diagnoses, 91% due to reporting ultrasound normal variants. The percentage of prenatal notifications rose from 48% in 1991-93 to 83-88% from 1996 to 2003 and dropped to 61% in 2006-08, partly reflecting changes in the reporting of normal variants. Reporting these increased the prenatal diagnosis rate from 53 to 63% with an increase in false-positive rate from 0.09 to 1.04%. A total of 722 (44% of prenatally detected affected fetuses) resulted in termination; 48% of these had chromosome anomalies, 34% had isolated structural anomalies, 7% had multiple anomalies, 10% had familial disorders; 42% had lethal anomalies and 58% would probably have survived the neonatal period giving an estimated 20% reduction in birth prevalence of congenital anomalies compatible with survival because of terminations.

Conclusion: There has been an improvement in prenatal detection of congenital anomalies over the two decades studied. The recognition that reporting normal variants, although increasing prenatal detection rates, leads to an increase in false-positive diagnoses has had an impact on practice that has redressed the balance between these two effects.