CAN FETAL ILIAC BONE-MEASUREMENT BE USED AS A MARKER FOR DOWNS-SYNDROME SCREENING

Objective The aim of this study was to assess the application of iliac bone length measurement in screening for Down's syndrome. Design Meas urement of fetal iliac bone length was prospectively carried out in 60 9 pregnant women at the time of amniocentesis, and correlated with the results of karyotype analysis. Subjects Following exclusion of cases with chromosomal abnormalities other than trisomy 21, cases with intra uterine growth impairment ol structural abnormalities and cases with i ncomplete follow-up, 466 karyotypically normal fetuses and 14 fetuses with trisomy 21 were included in the analysis. Methods Gentiles, stand ard deviations, expected values by means of linear regression analysis of the iliac bone, in relation to the biparietal diameter; were calcu lated in the normal fetuses. In order to identify pregnancies at risk for trisomy 21, where a 'longer' than normal iliac bone was expected, three cut-offs previously proposed by other authors and three new crit eria were employed. Sensitivity, false-positive rate and likelihood ra tio were calculated to assay the different cut-off criteria. Results E leven of the 14 (79%) fetuses affected by trisomy 21 had an iliac bone length greater than the 50th centile of normal values. The most usefu l threshold was an iliac bone length greater than or equal to 2 SD of the normal (29% sensitivity and 2 % false-positive rate). Conclusions This study confirms that fetuses with Down's syndrome tend to have a l onger iliac bone length measurement than those with normal karyotype. However, due to the differ ent methods used in different centers, the application of this measurement does not offer sufficiently convincing results for it to be used when screening fbr Down's syndrome.