PARENT PREFERENCES AND PRENATAL TESTING FOR NEURAL-TUBE DEFECTS

Previous analyses of prenatal screening for neural tube defects have g enerally found benefits to exceed costs. The usual screening battery f ollows an elevated maternal serum alphafetoprotein level with high res olution ultrasound and/or amniocentesis. Current thinking focuses on w eighing the risk of a false-negative (an abnormality missed) against t he risk of an amniocentesis-induced fetal loss. This thinking neglects the risk of a false positive (an unaffected fetus labeled abnormal) a nd individual parents' preferences concerning a false-negative us a fe tal loss. With these risks included, we find that high resolution ultr asound is appropriate for all women with elevated serum alpha-fetoprot ein. Women with moderately elevated serum alpha-fetoprotein who have n egative ultrasound scans need no further testing, nor do women with hi ghly elevated serum alpha-fetoprotein and positive ultrasound scans. F urther testing using amniocentesis to confirm the ultrasound result is appropriate for women with moderately elevated serum alpha fetoprotei n and positive ultrasound scans, and for women with highly elevated se rum alpha-fetoprotein and negative ultrasound scans. The actual cutoff s defining normal, moderately elevated, and highly elevated serum alph afetoprotein depend on several parameters, particularly the underlying prevalence of neural tube defects and the parents' preferences.