Cost-effectiveness of estimating gestational age by ultrasonography in Down syndrome screening.

OBJECTIVE To quantify the financial benefits of using ultrasound estimation of gestational age in maternal serum screening for Down syndrome. METHODS Maternal age-specific sensitivity and false-positive rates for Down syndrome were derived for the triple test (alpha-fetoprotein, hCG, and unconjugated estriol) using gestational age based on ultrasound dating and also time from the last menstrual period (LMP). These rates were entered into a formula to determine the societal financial net benefit of Down syndrome screening. The average per-case net benefits of ultrasound- and LMP-dated pregnancies were then compared. Average net benefits were also calculated separately with ultrasound versus LMP dating for triple tests referred to our laboratory, and the additional costs associated with any post-test ultrasound scans, repeat testing, or recalculations were estimated. RESULTS The use of ultrasound dating resulted in higher detection rates for Down syndrome and lower false-positive rates, which translated into an average per-case savings to society of $33.54. For women referred to our program with LMP dating, there was an average reduction of $31.60 in net benefits, plus added costs of $14.39 attributable to extra ultrasound, repeat testing, and recalculation. CONCLUSION When ultrasound dating is available before serum screening, it should be used preferentially to establish Down syndrome risk. Routine first-trimester ultrasound examination can be justified for women with a known LMP if the cost of the ultrasound examination is less than $46.