Ketupanya, A., and B. Crandall. “Comparison of Amniotic Fluid Alpha-Fetoprotein and Gel-Acetylcholinesterase Tests With Fetal Blood Contamination”. Thai Journal of Obstetrics and Gynaecology, vol. 1, no. 1, Jan. 1989, pp. 1-5, https://he02.tci-thaijo.org/index.php/tjog/article/view/257912.