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Which steps in human reproduction must work properly for pregnancy to begin?
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infertility
Major structures and hormones involved in the initiation of pregnancy. Also seen, at right, is the development of an egg cell (ovum) from follicle to embryo.
For pregnancy to begin, several complex biological steps must occur in sequence within the human reproductive system. When any of these processes are disrupted, it may result in infertility. The essential steps include:
- Ovulation: A mature egg must be released from the ovary. This process is regulated by hormones, including follicle-stimulating hormone and luteinizing hormone.12
- Fertilization: Sperm cells must be deposited into the female reproductive tract, travel through the uterus, and successfully unite with the egg, typically within the fallopian tube.32
- Transport: The resulting zygote must be transported through the fallopian tube toward the uterus while undergoing cell division.432
- Implantation: The developing embryo must attach to and embed itself into the uterine lining (endometrium). This step requires the uterus to be properly prepared by the hormone progesterone, which ensures the lining is receptive to the embryo.432
If these stages—from the maturation and release of the egg to the successful implantation of the embryo—do not function correctly, the biological initiation of pregnancy cannot be achieved.2