Early pregnancy screening for fetal aneuploidy with serum markers and nuchal translucency - de Graaf, I M; Pajkrt, E; Bilardo, C M; Leschot, N J; Cuckle, H S; van Lith, J M (Prenat Diagn, 1999)
. Doi: 10.1002/(SICI)1097-0223(199905)19:5<458:AID-PD569>3.0.CO;2-A