How Ageing Affects Fertility
For many women, one of the biggest fears associated with ageing is the loss of fertility. With changes in modern society promoting women’s liberation and enabling women to have options outside being a housewife and mother, many women have put off having children in favour of career, education or other pursuits.
A result of this phenomenon is increasing rates of infertility and fertility problems as women discover that their ability to conceive and have a healthy baby diminishes significantly with age.
A study published in 1957 (Tietze C: Reproductive span and rate of conception among Hutterite women. Fertility and Sterility 1957;8:89-97) showed that at age 30, only 7% of couples were infertile – however, by age 40, this number had risen to 33% (over third of the population) and by age 45, over 87% of couples were infertile. Since then, more research has indicated that infertility rates have risen even higher in the general population in many developed societies.
Egg Quantity and QualityThe real issue affecting fertility is actually not the number in a woman’s age per se but the quantity and quality of a woman’s eggs. For example, a 43 year old woman may still have an abundant supply of unusually good quality eggs whilst a 25 year old woman may have very poor quality eggs and be less fertile.
However, these are the exceptions rather than the rule and in general, egg quality and quantity tends to decline significantly when a woman reaches her late 30’s and more rapidly as she enters her early 40’s. And since problems of egg quantity and quality tend to be more common in older woman, it can generally be said that female fertility problems increase significantly with age.
So why does a woman’s eggs deteriorate as she ages? This is due to the fact that every woman is born with her full complement of eggs at birth – she cannot be “resupplied” if she runs out or the eggs deteriorate in quality. These eggs sit in the ovaries and are released, usually one at each menstrual cycle, for potential fertilisation.
Meanwhile, however, the main supply continually ages in the ovaries. Therefore, by the time a woman reaches her 30’s, her supply of eggs will have already diminished and what is left may have aged and declined significantly in quality.
Interestingly, men produce new sperm constantly, following the onset of puberty, and therefore there is no supply that is ageing. Consequently, the older men do not have substantially reduced fertilising potential although that fact that older men tend to be less sexually active may be a factor in lower chances of conception.
Genetic Abnormalities in Ageing EggsIn addition to a decline in quantity and general quality, older eggs also display an increased incidence of chromosomal abnormalities. This is due to abnormalities in the meiotic spindle which is involved in organising the chromosome pairs in the DNA, during egg development.
These abnormalities increase with a woman’s age – research shows that only 17% of eggs from women in their early 20’s had abnormalities, compared to 79% of eggs from women in their early 40’s. Thus, as women get older, they have a higher chance of producing chromosomally abnormal eggs which in turn leads to lower chances of conception, increased risk of miscarriage and a higher chance of babies born with genetic abnormalities and developmental problems (e.g. Downs Syndrome).