Following fertilization and early cleavage divisions, what prevents premature implantation of a blastocyst in the fallopian tube, rather than the uterus?

💡 Explanation

Proper blastocyst implantation in the uterus depends on successful sequential interactions between the trophoblast and endometrium, including L-selectin mediated adhesion. Because the correct glycans are expressed later in the uterus rather than the fallopian tube, premature implantation is prevented. Therefore, the answer is trophoblast L-selectin binding, rather than premature prostaglandin action.

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