Screening for trisomy 21 by measuring nuchal translucency during the first trimester of pregnancy
Charasson, T.; Ko-Kivok-Yun, P.; Martin, F.; Sarramon, M.F.
Journal de Gynecologie Obstetrique et Biologie de la Reproduction 26(7): 671-678
1997
ISSN/ISBN: 0368-2315 PMID: 9471429 Document Number: 480785
The purpose of the present literature review is to assess the screening value of trisomy 21 by measurement of fetal nuchal translucency (NT) thickness in the first trimester. NT is a subcutaneous translucency between the skin and the soft tissues overlying the cervical spine, which disappears in the second trimester. Ultrasound examination was used to image a sagittal section of the fetus to measure the maximum thickness of the subcutaneous translucency. NT is physiological for a measurement < 3 mm but the incidence of chromosomal abnormalities (essentially trisomies 21, 18 and 13) increases when NT gtoreq 3 mm. Differential diagnoses include cystic hygroma and fetal hydrops. For screening purposes, a cut-off threshold value of gtoreq 3 mm, with a standardized technique, gave a sensitivity gtoreq 50%, a false positive rate < 5% and a positive predictive value > 1%. In the chromosomally normal group, prognosis was good, but incidence of structural defects and fetal loss increased, with a sharp rise in these complications for fetal translucency thickness gtoreq 5 mm.