Integrated serum screening for Down syndrome in primary obstetric practice

Abstract

Objectives: Integrated serum screening for Down syndrome is potentially more effective than current second-trimester screening. We report results of an intervention trial of integrated serum screening that involved 229 primary prenatal care practitioners throughout Maine.

Methods: Women provided a first-trimester serum (for PAPP-A) followed by a second-trimester serum (for AFP, uE3, hCG, and DIA). These five marker measurements were used to calculate a Down syndrome risk in the second trimester. Screen-positive women (risk > or = 1:100) were managed according to standard practice.

Results: During 24 months' enrollment, 11 159 women provided a first-trimester sample (61% of women receiving screening services). Nine thousand seven hundred twenty-three women also provided a second-trimester sample; 8773 women satisfied gestational age criteria for testing in both trimesters. Integrated serum screening detected 14 of 16 Down syndrome cases (87%) and 79% after adjustment for trimester-of-ascertainment bias. The initial false-positive rate was 3.2% and was 2.7% when restricted to ultrasound-dated pregnancies. Performance was better than any combination of second-trimester markers. Implementation challenges included initial samples being collected too early and sample matching.

Conclusions: Integrated serum screening for Down syndrome was successfully implemented in primary care settings; screening performance was consistent with predictions. It provides an accessible and acceptable alternative to screening protocols that require nuchal translucency measurements.