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Which steps must occur for a pregnancy to begin successfully?
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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 a pregnancy to begin successfully, a series of precise biological steps must occur:
- Ovulation: A mature egg is released from the ovary and travels into the fallopian tube.1
- Fertilization: Sperm cells travel through the female reproductive tract to the fallopian tube, where one sperm penetrates the egg. Their nuclei merge to form a zygote, which contains the full complement of genetic material.623
- Cell Division: The zygote undergoes a series of mitotic divisions as it travels toward the uterus, developing into a morula and eventually a blastocyst.452
- Preparation and Implantation: The uterine lining (endometrium) must be prepared by the hormone progesterone to be receptive. The blastocyst then attaches to and embeds itself into the uterine wall. Many medical professionals consider this implantation the true beginning of pregnancy, as it establishes a connection to the mother and triggers essential hormonal changes.642