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Second-trimester levels of pregnancy-associated plasma protein-A and free beta-hCG in pregnancies with trisomy 13.
Spencer K, Crossley JA, Aitken DA, Nicolaides KH.
Prenat Diagn 2005;25:358-61. -
Screening for trisomy 13 by fetal nuchal translucency and maternal serum free beta hCG and PAPP-A at 10-14 weeks of gestation.
Spencer K, Ong C, Skentou H, Liao AW, Nicolaides KH.
Prenat Diagn 2000;20:411-6.