A screening program for trisomy 21 at 10–14 weeks using fetal nuchal translucency, maternal serum free ß-human chorionic gonadotropin and pregnancy-associated plasma protein-A. - Spencer, K.; Souter, V.; Tul, N.; Snijders, R.; Nicolaides, K. H. (Ultrasound in Obstetrics & Gynecology, 1999)