Nuchal thickness, urine beta-core fragment level, and maternal age for Down syndrome screening

OBJECTIVE: Our purpose was to report the midtrimester Down syndrome screeni ng efficiency of a 2-analyte algorithm, urine beta-core fragment (a metabol ite of human chorionic gonadotropin) and nuchal thickness, along with mater nal age in a high-risk population undergoing genetic amniocentesis. METHOD: Nuchal thickness, humerus length, and maternal urine beta-core frag ment levels were measured prospectively before genetic amniocentesis in 136 0 singleton pregnancies, 21 (1.5%) of which had fetal Down syndrome. All an alyte levels were expressed as multiples of the normal medians based on bip arietal diameter. Backward-stepwise logistic regression was used to determi ne whether the markers were significant independent predictors of fetal Dow n syndrome. Matrix analysis was used to calculate an adjusted Down syndrome likelihood ratio for each patient based on the significant screening marke rs. Multiplication by age-related midtrimester risk gave the adjusted Down syndrome risk. The sensitivity and false-positive rates at different Down s yndrome screening thresholds were used to generate a receiver-operator char acteristics curve. The area under the curve was used to assess the value of this screening test. RESULTS: On the basis of logistic regression, beta-core fragment level (p < .00001), nuchal thickness (P < .00001), and maternal age (P < .03), but no t humerus length (P = .332), were significant predictors of Down syndrome. At an adjusted risk threshold of > 1/60 the sensitivity and false-positive rate for Down syndrome were 85.7% and 4.9%, respectively, when beta-core fr agment level, nuchal thickness, and maternal age were used. Correspondence screening values at a risk threshold > 1/150 were 95.2% and 10.8%, respecti vely. The area under the receiver-operator characteristics curve was 0.9357 (SE = 0.0137), indicating that the algorithm is excellent for Down syndrom e screening. CONCLUSION: In this study, a combination algorithm consisting of nuchal thi ckness, urine beta-core fragment level, and maternal age had a high screeni ng efficiency for Down syndrome. This algorithm should be investigated as a new option for women at high risk of having a fetus with Down syndrome.