Implantation refers to the process where a fertilized egg, or ovum, attaches itself to the uterus wall. This typically takes place about six days post-fertilization when the blastocyst, or early stage embryo, comes in contact with the wall of the uterus.
As the embryonic cells continue to divide, the outer cell layer invades the uterine lining to procure oxygen and nutrients from the mother’s blood; this layer eventually develops into the placenta. Typically, the embryo implants in the upper portion of the uterus. However, if it implants lower near the cervix, a condition called placenta praevia might occur. In rare instances, implantation can take place outside the uterus, perhaps in a fallopian tube, leading to an ectopic pregnancy.