Human Growth and Development

Prenatal Development-Embryonic Period

When does implantation occur?

Implantation, the attaching of the blastocyst to the endometrium of the uterus, begins about six to seven days following fertilization. By day nine, the blastocyst is completely enclosed by endometrial cells and is implanted in the uterus. Only after the blastocyst is implanted in the uterus can a pregnancy continue.


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