Michael Carroll, a Reader and Associate Professor in Reproductive Science at Manchester Metropolitan University, looks at the differences between fertility in men and women, and the impact age has on both sexes.
Sputnik: How does age affect fertility for men?
Michael Carroll: Normally, age has a very limiting factor for women and the whole idea of infertility has always been focused around women but it's been coming to light now that men do provide a sperm, and you need a sperm and an egg, 50/50, and infertility is a 50/50 thing. It's both male and female. It's a couple’s issue. To focus on the male as a source of infertility, or wanting to find a cause of infertility has come to light, and rightly so. So, how does age affect it? Men can produce sperm from puberty right up to very old age. Now, they can produce sperm and the sperm are motile, which means they can swim, and they can reach an egg in the female's reproductive tract. But the quality of the sperm and the number of sperm produced changes with age, it's not an abrupt stop, but there is a decline in sperm quality, in how well the sperm swim that is the motility, on the shape of the sperm the morphology, and how much sperm are produced by the testes, and that's all down to a number of things. Age, the whole ageing process, bodies get older cells kind of atrophy, they get smaller, the testes become smaller as well, the amount of testosterone decreases with age and that can have an impact on the number of sperm that's produced. One of the things that's coming to light is not just the quality of the sperm in terms of how we look at it and how it swims but the genetics of the sperm, the DNA, and how that can change over time. So, it is an accumulation of mutations and DNA damage that occurs in men over time and older men past the age of 40,45, tend to have a higher increase in the DNA damage in their sperm.
Sputnik: Looking back to women, is this the same for women, are these changes the same for women with their egg supplies and their fertility as well?
Michael Carroll: All the eggs a woman will ever have are produced when she's a baby in the uterus. A female foetus at 20 weeks will probably have maybe 7 million of these immature eggs, and by the time she's born there's probably a million left, and by the time she reaches puberty, there are about maybe 400,000 of these eggs, it's just a very steep decline. It happens before they're born and this is a uniquely female thing, men produce sperm continuously throughout their lives, but it's a uniquely female thing. So, the two things that affect women's fertility and explain their very finite fertile window from puberty right to about late 40/50, is the number of eggs that she has which is called an ovarian reserve, and the quality of the eggs that she had, and both of those things combined limit a woman's capacity to reproduce past a certain age. It's not so clear cut in men as it is women.
Sputnik: What changes to fertility are experienced by older fathers, and when I say changes, are there any negative effects for example?
Michael Carroll: Couples are having babies later in life now. So, with that delay in having a child, there is an increase in the damage to the sperm as I mentioned earlier. What it does is if the sperm can't swim very well, they have a lower capacity to reach an egg. It's quite an arduous journey to find an egg in the female reproductive tract, it's a long journey, and sperm are amazingly specialised cells. They're the only cell that's produced by mammals or animals that reproduce internally, that are actually designed to live in another body, but they meet a lot of challenges within the female reproductive tract. The best sperm are the ones that reach the egg. So, having a good shape, the morphology of the sperm is important, being able to swim really good and respond to signals in the female reproductive tract is really important, and having good intact high-quality DNA from endosperm is important as well. These are the things that are impacted as men get older. The other thing to bear in mind is the psychosocial effects of male childlessness. So, when people are delaying their chances to have a family or start a family, what they're doing is they're decreasing starting a family and it's often not considered when people are having careers, and if they're young during their 20s and 30s. Until they reach a time when they've decided to have a family and then it doesn't happen because of these accumulated damaging effects that age has on both male and female, and that can have a serious psychosocial effect, especially with men because the whole idea of infertility and infertility treatment under discussion on infertility is very much female-based, so women-focused, but men tend to be on the periphery of this and they're not brought into this discussion as much and they tend to keep it to themselves as well.
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