Fewer women aged 35 and older choose serum screening for Down's syndrome: Impact and implications.

OBJECTIVE

To quantify changes in the proportion of women aged 35 and older choosing serum screening for Down's syndrome over time and the effect on false positive and detection rates.

METHODS

From Rhode Island hospital-based laboratory prenatal screening records (2013-2017) we extracted the test performed (Integrated, Combined, Quadruple), maternal age, and Down's syndrome risk; documented observed changes in maternal age distributions and false positive rates, and modelled the impact of varying proportions of older women choosing screening on each test's performance using the 2015 United States birth cohort as baseline.

RESULTS

Over five years, observed false positive rates for Integrated testing declined from 1.9 to 1.3% (-32%). The proportion of older women tested declined from 14.9 to 8.5%, from which modelling predicts a 16% decline in the false positive rate. This is lower than our observed change but consistent with a reduction driven by declining participation by older women. Modelling predicted a detection rate reduction from 89 to 87%. Larger detection rate impacts were predicted for Combined and Quadruple testing.

CONCLUSIONS

This study documents, for the first time, the declining proportion of older women choosing Down's syndrome serum screening and subsequent impact on screening performance. The American College of Obstetrics and Gynecology recommends offering cell-free DNA screening for these 'high risk' pregnancies and uptake may increase further. Screening programmes could consider increasing use of Integrated testing over other serum screening tests or lowering risk cut-offs so false positive rates approach those of 2012 to regain lost detection.