The uterus is like a piece of soil, and the embryo is like a seed. After the seed enters the soil, part of it continues to take root in the soil and connects with the placenta, while another part splits into new life.
How a seed chooses where to land surely depends first on where the soil is good for landing. Generally speaking, it's on the posterior, anterior, and lateral walls of the uterus, where the soil is vast and options are plenty. Only when these places are completely destroyed, with no options left, can the seed be forced to migrate to the lower segment. Therefore, factors like infection, multiple births, IUDs, multiple curettages, and cesarean sections—these surgery types that damage the soil—are all reasons that force the seed to wander to the lower segment.
