van Wijk, I J, Griffioen, S, Tjoa, M L, Mulders, M A, van Vugt, J M, Loke, Y W & Oudejans, C B 2001, ' HLA-G expression in trophoblast cells circulating in maternal peripheral blood during early pregnancy ', American Journal of Obstetrics and Gynecology, vol. 184, no. 5, pp. 991-7 . https://doi.org/10.1067/mob.2001.112973 American Journal of Obstetrics and Gynecology, 184(5), 991-7. Mosby Inc.