1. Combining maternal age and serum alpha-fetoprotein to predict the risk of Down syndrome;Hershey;Obstet Gynecol,1986
2. Maternal serum screening for fetal Down syndrome in women less than 35 years of age using alpha-fetoprotein, hCG, and unconjugated estriol: a prospective 2-year study;Phillips;Obstet Gynecol,1992
3. Clinical experience with the triple test for Down's syndrome screening;Thornton;J Perinat Med,1991
4. Increased fetal nuchal translucency at 11-14 weeks;Nicolaides;Prenat Diagn,2002
5. First and second trimester antenatal screening for Down's syndrome: the results of the Serum, Urine and Ultrasound Screening Study (SURUSS);Wald;Health Technol Assess,2003