Down syndrome screening using first-trimester combined tests and contingent use of femur length at routine anomaly scan

Authors

  • Laurent J. Salomon,

    Corresponding author
    1. Department of Obstetrics and Gynecology, University Paris Descartes, Necker-Enfants Malades Hospital, Assistance Publique-Hôpitaux de Paris, Paris, France
    • Department of Obstetrics and Gynecology, University Paris Descartes, Necker-Enfants Malades Hospital, Assistance Publique-Hôpitaux de Paris, 75015 Paris, France.
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  • Sylvie Chevret,

    1. Department of Biostatistics, Saint Louis Hospital, Assistance Publique-Hôpitaux de Paris, Paris, France
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  • Laurence Bussieres,

    1. Department of Obstetrics and Gynecology, Reproductive Biology and Cytogenetics, Poissy-Saint Germain Hospital, University Versailles-St Quentin, Poissy, France
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  • Yves Ville,

    1. Department of Obstetrics and Gynecology, University Paris Descartes, Necker-Enfants Malades Hospital, Assistance Publique-Hôpitaux de Paris, Paris, France
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  • Patrick Rozenberg

    1. Department of Obstetrics and Gynecology, Reproductive Biology and Cytogenetics, Poissy-Saint Germain Hospital, University Versailles-St Quentin, Poissy, France
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Abstract

Objective

The objective of this study was to evaluate the performance of the contingent use of femur length (FL) at routine mid-trimester scan in screening for Down syndrome (DS) in women having previously undergone first-trimester screening with disclosure of risk estimates.

Methods

Data from a prospective screening trial for DS in a population of 21 492 women with 80 observed DS were used. The performance of a contingent screening strategy based on adding short FL (FL < 5th percentile) as a soft marker in women at intermediate first-trimester risks was evaluated through simulated data.

Results

In our population, the median (25th–75th percentile) maternal age was 30.7 years (28.0–33.9; range: 18.0–46.3). The median (25th–75th percentile) gestational age at ultrasound examination was 12 weeks 3 days (12 weeks and 12 weeks 6 days; range: 11 weeks to 13 weeks 6 days). Contingent screening allowed an improvement in screening performance. For example, using a first-trimester risk cut-off of 1/100 and an intermediate-risk population within (1/1000, 1/100) for the search of FL, a sensitivity (Se) of 88.4% at a 3% false-positive rate (FPR) was reached. With a cut-off of 1/200 and an intermediate-risk population within (1/1000, 1/200), screening would allow an Se of 92.3% at a 4% FPR.

Conclusions

Contingent screening could be used following first-trimester combined screening followed by second-trimester ultrasound soft markers. This could identify indications for early invasive testing in the highest risk cases and would allow efficient and simple ultrasound-based screening in the second trimester. This would provide an 88.4% Se for a 3% FPR, at no additional cost as compared to first-trimester combined screening and routine mid-trimester scan. Copyright © 2010 John Wiley & Sons, Ltd.

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