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

Objective: To quantify the financial benefits of using ultrasound estimatio n of gestational age in maternal serum screening for Down syndrome. Methods: Maternal age-specific sensitivity and false-positive rates for Dow n syndrome were derived for the triple test (alpha-fetoprotein, hCG, and un conjugated estriol) using gestational age based on ultrasound dating and al so 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 s eparately with ultrasound versus LMP dating for triple tests referred to ou r laboratory, and the additional costs associated with any post-test ultras ound scans, repeat testing, or recalculations were estimated. Results: The use of ultrasound dating resulted in higher detection rates fo r Down syndrome and lower false-positive rates, which translated into an av erage per-case savings to society of $33.54. For women referred to our prog ram with LMP dating, there was an average reduction of $31.60 in net benefi ts, plus added costs of $14.39 attributable to extra ultrasound, repeat tes ting, and recalculation. Conclusion: When ultrasound dating is available before serum screening, it should be used preferentially to establish Down syndrome risk. Routine firs t-trimester ultrasound examination can be justified for women with a known LMP if the cost of the ultrasound examination is less than $46. (C) 1999 by The American College of Obstetricians and Gynecologists.