Prenatal screening for Down syndrome in England and Wales and population-based birth outcomes.

Objective: Whether the introduction of antenatal screening for Down syndrome in England and Wales with serum biochemistry or ultrasound has led to improvements in patient outcomes is unknown. The purpose of this study was to relate pregnancy outcomes to the dominant method used for prenatal Down syndrome screening.

Study Design: For the years 1989 through 1999, England and Wales were divided into geographically defined areas where specific hospitals, health authorities, and cytogenetic laboratories provided maternity care for well-defined populations. For each year from 1989 through 1999, the dominant Down syndrome screening method that was used in each area was determined. Outcomes for area-years that used serum biochemistry or ultrasound (first or second trimester) were compared with area-years that used advanced maternal age as the dominant screening method. The percent of Down syndrome cases that were diagnosed prenatally (effectiveness) and the number of invasive prenatal tests that were performed to diagnose each Down syndrome case prenatally (efficiency) were compared.

Results: There were 5,980,519 births and 335,184 referrals for prenatal karyotyping (amniocentesis and chorionic villus sampling) that occurred in the area-years studied, of which 12,047 pregnancies were diagnosed as Down syndrome; 5393 cases of Down syndrome (45%) were diagnosed prenatally. Invasive testing increased from 4.4% of pregnancies in 1989 to 6.4% in 1997 and declined slightly in 1999 (5.8%). Prenatal diagnosis of Down syndrome cases rose from 28% in 1989 to 53% in 1999, and the number of invasive tests that were performed to diagnose each Down syndrome case fell from 89.7 to 47.7 (P [for trend]<.0001). Areas with serum or ultrasound as the dominant screening method detected 50% more Down syndrome cases in prenatally (52% and 53% vs 36%; P<.0001) and performed fewer invasive procedures to diagnose each Down syndrome case (60.7 and 52.0 vs 88.0; P<.0001) compared with areas in which advanced maternal age screening was dominant, despite serving populations with similar mean/median maternal ages.

Conclusion: In clinical practice, screening programs for Down syndrome that were based on maternal serum biochemistry or ultrasound were more effective and efficient than the screening programs that used advanced maternal age alone.