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First trimester prenatal diagnosis of trisomy 21 in discordant twins using fetal nuchal translucency thickness and maternal serum free beta-hCG and PAPP-A.
Spencer K, Nicolaides KH.
Prenat Diagn 2000;20:683-4. -
Maternal serum free beta-hCG at 10 to 14 weeks of gestation in trisomic twin pregnancies.
Noble PL, Snijders RJ, Abraha HD, Sherwood RA, Nicolaides KH.
BJOG 1997;104:741-3.