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While the effect of a woman's age on fertility and reproduction has been known for a long time, the impact of a man's age has been neglected until recently. Over the last fifteen years or so, medical and scientific teams have taken an interest in this subject and have analysed various indicators in their studies, such as sperm parameters, the couple's fertility, spontaneous miscarriages (SCC), and the health of the children.
Man's age: impact on fertility and sperm quality
Some studies have shown that a man's age reduces sperm volume, sperm mobility, the percentage of normal forms and, to a lesser extent, sperm concentration. This has a considerable impact on male fertility and reproduction. Several mechanisms have been suggested:
Man's age: impact on a couple's fertility
In the general population, several publications have shown that the impact of a man's age on a couple's fertility can result in an increase in the average time to conception beyond a paternal age of 40. In a fertility journey, an increased risk of conception failure at a man's age has also been demonstrated.
Man's age and spontaneous miscarriage (SCC)
Two major studies carried out in the general population have demonstrated an increased risk of spontaneous miscarriage (SCC) as the man's age increases.
Another study involving more than 21,000 intrauterine insemination cycles showed that the risk of SCC is increased by almost 2 times when men are aged 45 and over compared with men under 35, after adjustment for maternal age. In IVF/ICSI, the results are more contradictory.
Man's age and children's health
In addition to the impact of a man's age on fertility, paternal age is also thought to have an impact on the health of his offspring. In particular, an association has been shown between a man's age and an increased incidence in his offspring of rare autosomal dominant genetic diseases such as achondroplasia and Appert's syndrome, as well as complex diseases such as schizophrenia and autism.
Man's age: impact on sperm genome quality
These observations raise the question of the quality of the genome of the ageing spermatozoon. In humans, gamete formation is continuous from puberty onwards. Spermatogonia (primordial germ cells) undergo cell division approximately every 16 days, i.e. 23 cycles per year. Consequently, the number of cell divisions depends on age: at the age of 20, 150 cell divisions precede the formation of a spermatozoon, whereas, at the age of 50, 840 cell divisions precede the formation of a spermatozoon.
Thus, with age, the increase in the number of cell divisions during spermatogenesis contributes to an increased risk of de novo mutations (not present in the parents), as demonstrated by the study by Kong and colleagues in Nature in 2012.
Other studies have shown that the rate of fragmentation of sperm DNA (DNA breaks) increases with age, which could explain the fertility journey failures and the occurrence of FCS.
The effects of a man's age on reproduction are manifold:
While no critical threshold for paternal age has been clearly identified, the risks appear to be moderate between the ages of 40 and 50, and greater above the age of 50. Obviously, the cumulative effect of the ages of the 2 partners will have to be taken into account when assessing the risks.
