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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. -
Urinary beta-core hCG: screening for aneuploidies in early pregnancy (11-14 weeks gestation)
Macintosh MC, Nicolaides KH, Noble P, Chard T, Gunn L, Illes R.
Prenat Diagn 1997;17:401-5.