-
Screening for trisomy 21 in twin pregnancies in the first trimester: an update of the impact of chorionicity on maternal serum markers.
Spencer K, Kagan KO, Nicolaides KH.
Prenat Diagn 2008;28:49-52. -
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.