Second-trimester maternal serum screening for fetal Down syndrome: As a screening test for hemoglobin Bart's disease: A prospective population-based study.

Purpose: The purpose of this study is to determine the effectiveness of second-trimester maternal serum screening for Down syndrome as a screening test for fetal hemoglobin (Hb) Bart's disease among an unselected population.

Methods: A secondary analysis of a large prospective database (20 254 pregnancies) was conducted to compare the levels of maternal serum screening, alpha-fetoprotein (AFP), free beta-human chorionic gonadotropin, and unconjugated estriol between pregnancies with Hb Bart's disease and unaffected pregnancies.

Results: The median AFP levels were much higher among affected fetuses (1.