Monozygotic twins discordant for monosomy 21 detected by first-trimester nuchal translucency screening. - Cheng PJ; Shaw SW; Shih JC; Soong YK; Cheng, Po-Jen; Shaw, Sheng-Wen; Shih, Jin-Chung; Soong, Yung-Kuei (Obstetrics & Gynecology, 2006)