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Combining nuchal translucency and serum markers in prenatal screening for Down syndrome in twin pregnancies
Author(s) -
Wald Nicholas J.,
Rish Simon,
Hackshaw Allan K.
Publication year - 2003
Publication title -
prenatal diagnosis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.956
H-Index - 97
eISSN - 1097-0223
pISSN - 0197-3851
DOI - 10.1002/pd.627
Subject(s) - fetus , obstetrics , medicine , twin pregnancy , prenatal diagnosis , pregnancy , down syndrome , prenatal screening , nuchal translucency , nuchal translucency measurement , gynecology , biology , genetics , psychiatry
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.