What is implantation?

Hint: Implantation is the term which is for the process of attachment of blastocyst, which is the stage of an embryo formed in the fallopian tube travels to the uterus and attached to the endometrium of the uterine wall, and this happens after 7th day of fertilization.

Complete answer:
In humans or in any conceptus ( placental ) animal, the implantation begins after one week, and mostly range from 8 to 10 days. Before the implantation to start, there are certain changes that occur in the endometrium and this is called the implantation window, and the implantation occurs after a peak in the luteinizing hormone.

Endometrial changes occur after the ovulation is predecidualization and if the pregnancy confirms it enters the decidualization stage, where there is an increase in vascularization, and decidual cells become polyhedral shapes with large nucleus and glycogen storage.

The implantation starts with an initial stage called adaptation, in the first phase of adaptation, the blastocyst loosely adheres to the endothelium, and in the second phase, this blastocyst roll to the site of implantation, and firmly attached to the endometrial layer of the uterus, wherein the third phase there is adhesion and interaction of the blastocyst with uterus takes place.

The implantation should occur always in the body of the uterus, sometimes it does not happen it may implant in some loss wrong places like fallopian tubes occur, which is the abnormal implantation, and sometimes even if implantation is proper but placenta may not develop properly.

Note: In recent years, there is a new technology called Assisted reproductive technology, in this technique they introduce the blastocyst into the uterus, in order to allow the normal implantation, it is useful for people with pregnancy problems because of improper implantation.