Implantation failure can be divided into three areas.

Problems with the embryos
Problems with “host” uterus
Problems in the interaction between embryo and uterus.
Failure to achieve a pregnancy following 2-3 IVF cycles in which reasonably good [ high grade embryos] embryos were transferred is termed as implantation failure.
Embryonic loss which occurs repeatedly after Assisted Reproduction may be attributed to many factors.

These are grouped into three categories :-

Decreased endometrial receptivity
Embryonic defect
Factors with combined effect