Cocquebert M, Berndt S, Segond N, Guibourdenche J, Murthi P, Aldaz-Carroll L, Evain-Brion D, Fournier T. Comparative expression of hCG β-genes in human trophoblast from early and late first-trimester placentas. American Journal of Physiology-Endocrinology and Metabolism. 2012 Oct 15;303(8):E950–8. doi: 10.1152/ajpendo.00087.2012.