Parent preferences and prenatal testing for neural tube defects.

Previous analyses of prenatal screening for neural tube defects have generally found benefits to exceed costs. The usual screening battery follows an elevated maternal serum alpha-fetoprotein level with high-resolution ultrasound and/or amniocentesis. Current thinking focuses on weighing the risk of a false-negative (an abnormality missed) against the risk of an amniocentesis-induced fetal loss. This thinking neglects the risk of a false-positive (an unaffected fetus labeled abnormal) and individual parents' preferences concerning a false-negative vs a fetal loss. With these risks included, we find that high-resolution ultrasound is appropriate for all women with elevated serum alpha-fetoprotein. Women with moderately elevated serum alpha-fetoprotein who have negative ultrasound scans need no further testing, nor do women with highly elevated serum alpha-fetoprotein and positive ultrasound scans. Further testing using amniocentesis to confirm the ultrasound result is appropriate for women with moderately elevated serum alpha-fetoprotein and positive ultrasound scans, and for women with highly elevated serum alpha-fetoprotein and negative ultrasound scans. The actual cutoffs defining normal, moderately elevated, and highly elevated serum alpha-fetoprotein depend on several parameters, particularly the underlying prevalence of neural tube defects and the parents' preferences.