ABSTRACT
AIMS: This study compares different screening strategies for the detection of Down syndrome and considers practical implications of using multiple screening protocols. METHODS: The performance characteristics of each screening strategy were assessed based on datasets of Down syndrome (n=11) and unaffected pregnancies (n=1006) tested in both first and second trimester, as well as data from first trimester (n=18,901) and second trimester (n=40,748) pregnancies. RESULTS: For a detection rate of 91%, the false positive rates for integrated and serum integrated screening were 2.5% and 6.3%, respectively, compared with combined first trimester (4.6%) and second trimester (12.6%) screening. Contingent and sequential screening protocols achieved detection rates of 82 to 91% with false positive rates between 2.6 and 2.9%. Contingent protocols require retesting of 15 to 20% of cases in the second trimester. Sequential and integrated protocols require retesting of 98 to 100% of cases in the second trimester. The various screening strategies did not always detect the same Down syndrome pregnancies. CONCLUSIONS: Combining first and second trimester markers for Down syndrome screening better defines the at-risk population. However, integrated protocols complicate management of screening programs and may not be suitable as primary screening strategies. It may be a better use of resources to refine current first and second trimester programs through improved access and new markers. We therefore suggest thinking twice before embracing integrated population screening programs.
Subject(s)
Down Syndrome/diagnosis , Pregnancy Trimester, First/blood , Pregnancy Trimester, Second/blood , Prenatal Diagnosis/methods , Prenatal Diagnosis/standards , Adult , Biomarkers/blood , Down Syndrome/blood , False Positive Reactions , Female , Humans , Mass Screening/methods , Mass Screening/standards , Odds Ratio , Pregnancy , Reproducibility of Results , Risk Assessment , Sensitivity and SpecificityABSTRACT
OBJECTIVE: The purpose of this study was to review trends in the us of maternal serum Down syndrome screening and invasive prenatal testing before and after the introduction of a state-based first-trimester combined Down syndrome screening program. STUDY DESIGN: A retrospective population-based study was performed on first- and second-trimester Down syndrome screening, invasive prenatal testing, and prenatal detection of Down syndrome from 1995 to 2005 in South Australia with data from state-based registers. Chi-square tests were used to evaluate trends. RESULTS: There was a significant decrease in the use of second-trimester Down syndrome maternal serum screening (from 75% in 1995 to 25% in 2005; P < .001) and a corresponding significant increase in first-trimester combined screening (from 0.8% in 2000 to 49% in 2005; P < .001). The proportion of all confinements that involved invasive prenatal testing fell (from 9.3% in 1995 to 7.6% in 2005; P < .001). There was a significant decrease in the number of invasive prenatal tests that were needed to detect 1 Down syndrome fetus (from 86 tests in 1995 to 40 tests in 2005; P < .001), with no significant change in the proportion of Down syndrome cases that were detected prenatally. CONCLUSION: The introduction and increased use of first-trimester combined Down syndrome screening has been associated with more efficient use of invasive prenatal testing in South Australia and has maintained a high level of overall prenatal detection.
