Penttilä , I.M. et al. 1993. 6.1.3.2 Quality Specifications for S-AFP and S-HCG-β Determinations for Screening of Fetal Abnormalities. Upsala Journal of Medical Sciences. 98, 3 (Sept. 1993), 375–380. DOI:https://doi.org/10.3109/03009739309179335.