THE UTILITY OF FETAL BIOMETRY AS AN ADJUNCT TO THE MULTIPLE-MARKER SCREENING-TEST FOR DOWN-SYNDROME

OBJECTIVE: Our purpose was to investigate fetal biometry as an adjunct to the multiple-marker screen (maternal age, serum cu-fetoprotein, es triol; and human chorionic gonadotropin) for Down syndrome. STUDY DESI GN: Fifty-two cases of Down syndrome were compared with 7514 normal fe tuses. The measured/predicted femur length ratio had the best discrimi nant value (1.0 +/- 0.11 vs 0.93 +/- 0.13, p < 0.0001). Multivariate g aussian algorithms were developed and each computed a likelihood ratio for Down syndrome. The trivariate algorithm incorporated the three ma ternal analytes, whereas the quadripartite version also included the f emur length ratio. The study population included 38 cases of Down synd rome and 1098 euploid controls. The midtrimester risk was the product of the age-related risk and the likelihood ratio. RESULTS: The relativ e difference in the femur length ratio between normal and affected fet uses was small in comparison to that of the maternal serum analytes. A t a risk cutoff of greater than or equal to 1 : 190 the detection rate s Were similar and actually-favored the trivariate algorithm but diffe red only by one case of Down syndrome. CONCLUSION: The addition of the measure/predicted femur length ratio had a negligible effect on the p erformance of the multiple-marker screening test.