First- and second-trimester evaluation of risk for Down syndrome

Robert H. Ball, Aaron B. Caughey, Fergal D. Malone, David A. Nyberg, Christine H. Comstock, George R. Saade, Richard L. Berkowitz, Susan J. Gross, Lorraine Dugoff, Sabrina D. Craigo, Ilan E. Timor-Tritsch, Stephen R. Carr, Honor M. Wolfe, Danielle Emig, Mary E. D'Alton