The pre-embryonic structure that enters the uterus is a fluid-filled ball of cells called a

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The pre-embryonic structure that enters the uterus is called a blastocyst. The blastocyst is a fluid-filled ball of cells that is formed from the zygote after several cell divisions. The blastocyst consists of an inner cell mass that will eventually form the embryo and an outer layer of cells called the trophoblast that will form the placenta.

The Pre-Embryonic Structure That Enters the Uterus Is a Fluid-Filled