Where does Embryo Implantation occur?
According to Minami et al. (2003)1 (open access) the early gestational sac can be located by ultrasound, and usually is high in the uterus, more often on the left or right than in the middle.  They provide an illustration of the distribution.



 1. Minami, S., Ishihara, K. and Araki, T., 2003. Determination of blastocyst implantation site in spontaneous pregnancies using three-dimensional transvaginal ultrasound. Journal of Nippon Medical School, 70(3), pp.250-254.