1. Jorgensen PI, Trolle D. Low urinary oestriol excretion during pregnancy in women giving birth to infants with Down’s syndrome. Lancet. 1972;ii:782–4.
2. Nisula BC, Blithe DL, Akar A, Leport G, Wehmann RE. Metabolic fate of human choriogonadotropin. J Steroid Biochem. 1989;33:733–7.
3. Cole LA, Kardana A, Park S-Y, Braunstein GD. The deactivation of hCG by nicking and dissociation. J Clin Endocrin Metab. 1993;76:704–10.
4. Rotmensch S, Liberati M, Kardana A, Mahoney M, Cole LA. Peptide heterogeneity of human chorionic gonadotropin (hCG) and its β-subunit in down syndrome pregnancies. Am J Obstet Gynecol. 1992;166:354.
5. Cuckle HS, Pergament E, Benn P. Multianalyte maternal serum screening for chromosomal abnormalities and neural tube defects. In: Milunsky A, Milunsky JM, editors. Genetic disorders and the fetus: diagnosis, prevention and treatment. 7th ed. Hoboken: Wiley-Blackwell; 2016. p. 483–540.