Final answer:
The statement about the blastocyst implanting outside the uterine cavity, typically in the fallopian tube, is true and refers to an ectopic pregnancy. Normally, a blastocyst implants in the uterus, with failed implantations often leading to shedding during menses.
Step-by-step explanation:
The statement that a blastocyst implanting outside the uterine cavity, commonly in the fallopian tube, is in fact true. Normally, the blastocyst continues down the fallopian tube, reaching the uterus about 4 or 5 days after fertilization, where it should implant into the endometrium lining. When the blastocyst implants itself somewhere other than the uterus, such as the fallopian tube, it is referred to as an ectopic pregnancy. Ectopic pregnancies can also occur in other locations, like the ovarian ectopic pregnancy or abdominal ectopic pregnancy.
Blastocyst implantation usually takes place in the fundus or posterior wall of the uterus if the endometrium is ready and well-prepared to receive the blastocyst. However, if implantation does not occur due to the endometrium not being fully developed, the blastocyst may either detach to find a better implantation site or fail to implant altogether, leading to its shedding during menses.