Increasing detection rates of birth defects by prenatal ultrasound leading to apparent increasing prevalence. Lessons learned from the population-based registry of birth defects of Barcelona.

OBJECTIVE

To assess the evolving trends in prenatal ultrasound detection of birth defects and to suggest a method to avoid the bias generated by an increasing detection rate, when comparing different time periods.

METHODS

In the population-based registry of birth defects of Barcelona (REDCB), 1976 cases with birth defects (1462 newborns and 514 terminations of pregnancy) were observed among 99 753 pregnancies, from 1992 to 1999. Detection rates for isolated birth defects by anatomical systems were evaluated. Since an increasing prevalence was observed in some birth defects systems, adjustment for detection rates was suggested.

RESULTS

A rise in prevalence was observed in isolated birth defects involving internal organs (central nervous, respiratory, digestive, and urinary systems). Ultrasound detection rates increased in all system groups of isolated birth defects during the study period, except for cardiovascular defects. Early detection rates (before 23 weeks of pregnancy) increased in all but three systems (cardiovascular, genital and tegument).

CONCLUSIONS

The apparent rise in the observed prevalence of certain birth defects may be largely due to improvements in prenatal detection methods. Population-based registries are able to measure the impact of evolving prenatal diagnosis in order to avoid biases and establish the prevalence of birth defects more accurately.