-
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. -
A screening program for trisomy 21 at 10-14 weeks using fetal nuchal translucency, maternal serum free beta-human chorionic gonadotropin and pregnancy-associated plasma protein-A.
Spencer K, Souter V, Tul N, Snijders R, Nicolaides KH.
Ultrasound Obstet Gynecol 1999;13:231-7.