Final answer:
Implantation in pregnancy typically occurs around day 8 or 9 after fertilization, with the blastocyst embedding into the endometrium of the uterus. Successful implantation is crucial for pregnancy to proceed.
Step-by-step explanation:
Implantation in Pregnancy
Implantation typically occurs around day 8 or 9 after fertilization. It begins when the blastocyst, having shed its outer layer (zona pellucida), makes contact with the uterine wall and adheres to the endometrium. The cells of the trophoblast then embed into the uterine lining. The blastocyst may implant in the fundus or the posterior wall of the uterus but requires a fully developed endometrium to do so. If conditions are not ideal, the blastocyst will detach to find a more suitable location. A large percentage, 50-75%, of blastocysts fail to implant, resulting in their shedding during the menstrual cycle. This contributes to why achieving pregnancy many times necessitates multiple ovulation cycles.