Arends , J. et al. 1993. 6.1.2.3 Prenatal Screening for Neural Tube Defects, Quality Specification for Maternal Serum Alphafetoprotein Analysis. Upsala Journal of Medical Sciences. 98, 3 (Sept. 1993), 339–347. DOI:https://doi.org/10.3109/03009739309179330.