-
Sonographic screening for trisomy 13 at 11 to 13(+6) weeks of gestation.
Papageorghiou AT, Avgidou K, Spencer K, Nix B, Nicolaides KH.
Am J Obstet Gynecol 2006;194:397-401. -
Second-trimester levels of pregnancy-associated plasma protein-A and free beta-hCG in pregnancies with trisomy 13.
Spencer K, Crossley JA, Aitken DA, Nicolaides KH.
Prenat Diagn 2005;25:358-61.