Volume 23, Issue 7 p. 588-592
Original Paper

Combining nuchal translucency and serum markers in prenatal screening for Down syndrome in twin pregnancies

Nicholas J. Wald

Corresponding Author

Nicholas J. Wald

Wolfson Institute of Preventive Medicine, Bart's and the London School of Medicine and Dentistry, Charterhouse Square, London, UK

Wolfson Institute of Preventive Medicine, Bart's and the London School of Medicine and Dentistry, Charterhouse Square, London, UK.Search for more papers by this author
Simon Rish

Simon Rish

Logical Medical Systems, Newbury Street, London, UK

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Allan K. Hackshaw

Allan K. Hackshaw

Wolfson Institute of Preventive Medicine, Bart's and the London School of Medicine and Dentistry, Charterhouse Square, London, UK

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First published: 13 June 2003
Citations: 73

Abstract

A method is described to combine the ultrasound marker nuchal translucency (NT) with serum markers so that they can be used together in prenatal screening for Down syndrome in twin pregnancies. For monochorionic twin pregnancies (taken as monozygous), the two fetus-specific NT measurements are averaged before risk is calculated and before the contribution of the serum markers is incorporated. For dichorionic twin pregnancies (taken as dizygous), the risk for each fetus based on the individual NT measurements is calculated, the two fetus-specific risks are added together, and then the contribution of the serum markers is incorporated. In this way, all the screening markers can be used in combination to produce a pregnancy-specific ‘pseudo-risk’, rather than a fetus-specific pseudo-risk. We refer to pseudo-risk because in the absence of sufficient data on the screening markers in affected twin pregnancies, a true risk estimate cannot be calculated. Tentative estimates are given of screening performance in twins using NT, the combined test (NT with first-trimester serum markers), and the integrated test (NT with first- and second-trimester serum markers), all interpreted with maternal age. Copyright © 2003 John Wiley & Sons, Ltd.