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First-trimester maternal serum PAPP-A, SP1 and M-CSF levels in normal and trisomic twin pregnancies.
Bersinger NA, Noble P, Nicolaides KH.
Prenat Diagn 2003;23:157-62. -
First trimester urine free beta hCG, beta core, and total oestriol in pregnancies affected by Down's syndrome: implications for first-trimester screening with nuchal translucency and serum free beta hCG.
Spencer K, Noble P, Snijders RJ, Nicolaides KH.
Prenat Diagn 1997;17:525-38.