The blastocyst reaches the uterus at roughly the fifth day after fertilisation, and implants into the uterine wall on about day six. At this point in the mother's menstrual cycle,
the endometrium (lining of the uterus) has grown and is ready to support a
fetus. The blastocyst adheres tightly to the endometrium where it receives
nourishment via the mother's bloodstream.

During the time between implantation and the eighth week, the cells are called an embryo.
So yeah up to a week after conception going by that.

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