Fertility is defined as the quality or state of being fertile. In other words, the ability to become pregnant, carry and give birth to a baby.

The Female Reproductive System

Females are born with about four hundred thousand oocytes, or immature female reproductive cells, which are then stored in the female's ovaries.  

It then becomes possible for a female to reproduce upon the commencement of her first menstrual cycle, which usually occurs around the age of twelve.  During each menstrual cycle, the female's ovaries will release at least one egg.

This is made possible also by the work of the hypothalamus and pituitary glands, which are located in the female brain. These glands produce follicles with the eggs inside of them, while the ovary simultaneously produces estrogen. Estrogen is responsible for signaling the uterus to produce the uterine lining. Towards the middle of the cycle, the follicle breaks open and the egg is released.

If the egg is not fertilized, once the egg is released, the uterine lining will shed and it comes out in the form of menstruation.

The Fertilization Process

If it so happens that after the release of such egg, it is fertilized by a male sperm, the female becomes pregnant.

The fertilization process commences when the female engages in sexual intercourse or undergoes artificial insemination. In order for the fertilization to be successful, it is required that only one sperm fuses with egg, otherwise, the result could be early embryonic death. The fertilization process also requires a capacitation period, wherein the sperm resides inside the ovary for a period of time, usually several hours.

Once fertilized, the egg will go through the uterus and divide multiple times, and simultaneously attach to the uterine lining of the uterus. That process is called implantation, after which an embryo is formed.