Learn about fertility

The ovaries are two almond-shaped organs on either side of your uterus. During a woman’s fertile years, an egg is usually released from one of your ovaries each month in a process called ovulation.

Ovulation typically occurs every 28 days. However, the length of this cycle varies from woman to woman and normally sits somewhere between 21 to 35 days. While many women experience regular cycles, some women ovulate less frequently.

Once released from the ovary, the egg travels via the fallopian tubes to the uterus (womb). If unprotected sexual intercourse has recently occurred, the egg may meet a sperm along the way, in which case, fertilisation may occur. If fertilisation has occurred, the fertilised egg (now called an embryo) continues its way to the uterus where it will embed and develop for the duration of the pregnancy (the lining of the uterus has thickened in preparation for this).

In the event that fertilisation does not occur, the woman sheds the thickened lining of the uterus by menstruating, i.e. she has her period.

Unlike men who continually produce sperm throughout their life, women have a limited reserve of eggs. Each female is generally born with between one and two million eggs. This reserve falls to around 25% by the time of puberty.

Declining fertility begins around the age of 32 and accelerates again at the age of 37. Eventually, a woman will reach menopause, signifying the end of ovulation and her fertile years. In Australia, this occurs around the age of 50.

The ovulation and menstruation processes are driven by hormones. Thus, disruptions in hormonal function can impair fertility. Similarly, successful fertilisation and implantation depend on a clear, open passage between the ovaries and uterus in order for an egg (or embryo) to travel to the womb – this means that any structural abnormalities in the female reproductive tract (e.g. endometrial growths) can block this process.

Sperm production begins in puberty. Sperm are produced in the testicles and travel via a series of passages to a structure called the epididymis. Here, the sperm mature until ejaculation, where they will pass through another series of passages to exit via the urethra (opening in the penis). During ejaculation, the sperm combines with fluid produced from a few male reproductive glands to form a fluid called semen.

Each sperm consists of a head, mid-piece and tail. This structure helps the sperm to propel itself through the female reproductive tract in order to meet the female’s egg and enable fertilisation to occur. This can be a treacherous journey – of the millions of sperm in the ejaculated semen, only a very small proportion will reach the egg and only one sperm will actually fertilise the egg.

This means successful fertilisation relies on a man having adequate numbers of sperm in his semen, as well as the sperm having normal shape and motility (movement). In the absence of these characteristics, infertility can result. Moreover, while men continue to produce sperm throughout the entirety of their life, the quality of their sperm diminishes with age.

Similar to females, the production of sperm is also driven by hormones. Therefore, disruption in hormonal function can impair a male’s fertility. Furthermore, anything that prevents the passage of sperm from the testicles into the female reproductive tract can also prevent successful fertilisation and conception.