Hou, Z., Romero, R., Uddin, M., Than, N.G. and Wildman, D.E., 2009. Adaptive history of single copy genes highly expressed in the term human placenta. Genomics, 93(1), pp.33-41.
Article Adaptive history of single copy genes highly expressed in th...
the authors identified at least ~4000 single-copy genes in mammals and ~200 from humans that are highly expressed in placenta. Maybe that is a good start. Best regards.