1. Down syndrome phenotypes: the consequences of chromosomal imbalance;Korenberg;Proc Natl Acad Sci U S A,1994
2. Mean age of mother, 1970–2000;Mathews;Natl Vital Stat Rep,2002
3. Efficacy of screening for fetal Down syndrome in the United States from 1974 to 1997;Egan;Obstet Gynecol,2000
4. Births: final data for 2002;Martin;Natl Vital Stat Rep,2003