Up to 20% of couples can have problems conceiving.
The most natural, fertile age of females is from the age of 15 until 25 years old, and from that point on it continuously declines. With the beginning of the climacteric period and the onset of menopause, natural fertility ceases.
For males, natural fertility slowly begins to decline from the age of 40 onwards, however there will be individual cases where this onset can certainly occur later.
Sterility and related issues are only looked into when no conception arises, despite a couple having had regular intercourse (at least twice a week) for one to two years.
Natural Causes of Infertility
The natural fertility of a couple – females respectively – inevitably has a direct effect on the ability to conceive.
The likelihood of falling pregnant is primarily dependant on the ages of the oocytes (immature ova or egg cells in females), and not necessarily on the endocrine function of the ovaries.
Male fertility may also decrease with advanced age, due to a decline of sperm quality and testosterone (primary male sex hormone) concentrations in the blood.
In short, natural infertility is predominantly determined by the age of the female, and the hence associated changes in the female organism.
The Expectation of Pregnancy
The normal expectation of conception for a healthy young couple (between the ages of 20 and 30), is 20% per menstrual cycle. This means that generally one conception should be expected for every five or six menstrual cycles, presuming regular intercourse is occurring.
However, as mentioned before, the natural fertility of females begins to decline over the course of the second decade of life. The chance for a woman between the ages of 35 and 39 to fall pregnant is only half as much as that compared to a 19 to 26 year old woman.
This is attributable to two crucial aspects:
The decrease in quantity of available oocytes. The quantity of available oocytes in a woman’s body is determined within the early human embryonic development in the uterus. At the time of birth, a female baby will have around 1 million oocytes stored in her uterus. Some 40,000 to 60,000 will still be left at the beginning of the female reproductive age, marked by a girl’s menarche. Each one of the oocytes is able to ovulate and possibly facilitate a subsequent pregnancy.
However, during follicle maturation - oocyte maturation respectively – oocytes perish, so that the amount of available oocytes decline with each menstrual cycle. As a result, the likelihood of successfully conceiving is reduced with increasing age.
The ageing process of the oocytes. Like all somatic cells, oocytes also age. In some circumstances, this can lead to changes and even the destruction of chromosomes. This is the reason why a great number of oocytes need to mature until eventually a healthy, fertilised one is able to lodge itself in the female uterus.
Henceforth, the ability to conceive and remain pregnant declines naturally with increasing age.