Fertilization

In reproduction, timing is everything. There are several processes that must occur at exactly the right time. Any variance in the necessary steps can interfere with fertilization and/or implantation, resulting in infertility.

Beginning on the first day of the woman’s menstrual cycle, the body starts to make and release increasing amounts of follicle-stimulating hormone (FSH). This hormone, produced by the pituitary gland at the base of the brain, causes the follicles to grow and produce estrogen.

The egg that is developing inside the follicle also begins to mature. During the average cycle, at around day 14, the pituitary gland releases a burst of another hormone called luteinizing hormone (LH); this process is referred to as the LH surge. LH stimulates the final maturation of the egg and starts the ovulation process, resulting in the release of a mature egg from the follicle. As the egg travels through the fallopian tube, the ovulated follicle forms a cyst known as the corpus luteum, which produces levels of another female hormone: progesterone. Progesterone aids in the preparation of the uterine lining for the soon-to-be fertilized embryo.

If there are sperm present in the fallopian tube, the egg may be fertilized, and the resulting embryo will pass through the fallopian tube and enter the uterus, where it will implant itself in the uterine wall and hopefully grow into a baby. If the egg is not fertilized, it will still travel to the uterus, but for a different reason. Approximately two weeks after ovulation, the uterus sends a signal to the ovary to decrease progesterone production since no pregnancy occurred. Menstruation, or the shedding of the lining of the uterus, will then follow. The cycle will start again the next month.

The next step in the reproductive process is Implantation.