杏吧原创

MY FATHER was 50 when I was conceived. My mother, at 39, was called an elderly primigravida, a term used to describe a woman who becomes pregnant for the first time at 35 or older. There is no name for the male equivalent, though my father was delighted to call himself an 鈥渆lderly primigravidad鈥�.

Jokes aside, we are used to thinking of fertility and healthy pregnancy as predominantly the domain of women, who are warned all too frequently of the dangers of leaving it too late to start a family. This hasn鈥檛 been the case for men.

But it might be time for a reality check. In recent months, a number of studies have been building a picture of a looming male fertility crisis. Sperm counts are dropping, and it turns out that for men 鈥� far from having all the time in the world to become dads 鈥� the clock is ticking too.

In a society where couples are choosing to conceive later in life, we are heading towards a perfect storm. 鈥淚f the decline in sperm counts is real, then the combination of this and our general desire to have our children later in life is a total disaster,鈥� says Allan Pacey at the University of Sheffield, UK.

The fact that women, but not men, are so regularly harangued about their fertility perhaps isn鈥檛 surprising when you consider that women are born with all the eggs they will ever have, which dwindle and age with time, while men produce sperm throughout adulthood (see 鈥�It takes two鈥�).

You might assume men have little to worry about. But if the latest headlines are to be believed, something is amiss. Perhaps the most striking news came in July, with the discovery that sperm counts have in richer countries in the past 40 years, and are continuing to fall by 1.6 per cent every year (no such decline was seen in poorer countries, although there are fewer studies to go on). The finding came from a review of more than 185 different studies of sperm concentration and total sperm count in men between 1973 and 2011. 鈥淭he results were truly shocking,鈥� says at the Hebrew University of Jerusalem, Israel, who led the analysis. 鈥淚 thought: I know something that the world needs to know. This is a clear and present danger that we are already facing.鈥�

This isn鈥檛 the first study to find that sperm counts are dropping, but previous efforts were considered controversial. This one is much larger, and addresses problems with the previous work 鈥� for instance making sure all the papers included in the review used the same techniques and, crucially, that they didn鈥檛 include men with known fertility problems.

Even Pacey, a self-confessed 鈥済rumpy sceptic鈥� about declining sperm, says that this research made him take notice. 鈥淚 have to admit that I thought, 鈥極h, there might be something in this now鈥�,鈥� he says. 鈥淚鈥檓 a reluctant convert, in some ways.鈥� Even so, he argues that the only way to prove conclusively that sperm counts are dropping would be to recruit large numbers of 18-year-old men each year for 10 years and count their sperm, thus building a picture of how it changes over time. He and others have proposed this kind of study, but not received funding.

In the meantime, the most crucial thing is the current sperm count levels, says Richard Sharpe, who studies male reproductive disorders at the University of Edinburgh in the UK. 鈥淎 substantial proportion of young men have a sperm count that will impair their fertility 鈥� and that is the most important factor in all this,鈥� he says.

鈥淎 substantial proportion of young men have a sperm count that impairs fertility鈥�

That鈥檚 backed up by studies in European countries such as Denmark, Finland, Estonia, Latvia, Lithuania and Germany over the past 15 years. 鈥淚n all countries large proportions of men have a semen quality that may negatively affect their fertility,鈥� says andrologist . 鈥淔or some 10 to 15 per cent, it may be so low that they need fertility treatment to become fathers; another 20 to 25 per cent could expect to experience a prolonged waiting time to pregnancy, compared to men with optimal semen quality.鈥�

What causes this, however, remains murky. 鈥淭he truth is that we don鈥檛 have a good answer,鈥� says Sharpe. The fact that sperm counts have dropped so fast over such short time scales suggests the causes are lifestyle and environmental, as genetic changes would take longer to be seen in the population.

One possible explanation lies in the fact that, even though men produce sperm throughout adulthood, their ability to do so is largely preprogrammed in the womb. The idea is that things like low sperm count can originate at this time, probably because of impaired production of male sex hormones by the testes, known as testicular dysgenesis syndrome (TDS), or a reduced number of sperm-supporting cells.

But we don鈥檛 know why some fetuses develop TDS while others don鈥檛. This is particularly difficult to research as there is a period of 20 or more years between its causes in the womb and when we see low sperm counts in adults. Studies that investigate these causes and follow up later in life are impossible to get funded, and retrospective studies are impossible to carry out, as women don鈥檛 record or later remember all aspects of their lifestyle and diet during pregnancy.

The exception to this is smoking, which women do remember. In the UK, for instance, 10.6 per cent of pregnant women were smokers at the time of their delivery between 2015 and 2016, in some areas. Four studies show that sons born to women who reported smoking heavily while pregnant have a sperm count than normal levels as adults. 鈥淭his is one of the best pieces of epidemiological evidence showing how fetal events might affect sperm count in adulthood,鈥� says Sharpe.

For other prospective environmental culprits, such as plastics, painkillers and potentially hazardous chemicals, researchers grow human testes cells in animal models. While exposure to plastics didn鈥檛 seem to have an effect, , since the majority of women use painkillers in pregnancy.

Hard to conceive

But J酶rgensen says that is problematic because this doesn鈥檛 give us the whole picture. 鈥淭he reality is that humans are surrounded by thousands of chemicals that don鈥檛 seem to pose any threat 鈥� but in combination, they do,鈥� he says.

Whatever the causes of TDS, its effects are lifelong: a man鈥檚 sperm production is capped at the limit preprogrammed in the womb. But it can go down. And one of the factors affecting this is age. The crucial difference with women鈥檚 biological clocks, however, is that these stop ticking with the menopause, whereas men鈥檚 clocks continue to tick until death, just a bit slower.

鈥淩egardless of a woman鈥檚 age, if her partner is older conception rates drop鈥�

It鈥檚 hard to test the effects of this 鈥渋n the wild鈥� but a recent study of 19,000 IVF cycles showed just how much of an . 鈥淩egardless of a woman鈥檚 age, if her partner was older, we often saw a decline,鈥� says Laura Dodge at Beth Israel Deaconess Medical Center, who led the study.

Her study didn鈥檛 find any clear age when that decline hits, but others have. When and colleagues at Reproductive Technology Laboratories in Los Angeles looked at sperm samples from 5081 men aged between 16 and 72, they found that . Others suggest 鈥� the cut-off age for sperm donation.

A man鈥檚 age doesn鈥檛 just affect conception rates, it also has a bearing on the health of the offspring. Studies have found that those born to fathers aged 45 and over are at an increased risk of psychiatric disorders including psychosis. And research looking at everyone born in Sweden between 1973 and 2001 found that when compared with a child born to a 24-year-old father, one born to a 45 year old is 3.5 times more likely to have autism, 25 times more likely to have bipolar disorder and 2.5 times more likely to attempt suicide or have a substance abuse problem.

The issues arise because sperm comes from the same population of stem cells in the testes for a man鈥檚 entire life. These have to replicate over and over, and with every cell division there is a chance of mutation. 鈥淭hey鈥檝e probably divided about 800 times by the time a man is 40, and a consequence of all that cell division is that errors start to creep into the process,鈥� says Pacey. This affects the genetic quality inside the sperm head, so that when a sperm meets an egg, it is less able to fertilise it. 鈥淎nd if it does the job, you鈥檙e more likely to have a child with a problem. It is a very, very small increased risk, but when you look at big population studies, you see it,鈥� says Pacey.

Should this change the way we think about fertility? In reality, the woman鈥檚 age has by far the most influence over the chances of a healthy pregnancy, but the father鈥檚 age matters more than we think. 鈥淔rom my experience, it seems people are still focused almost exclusively on the woman鈥檚 age,鈥� says Dodge. 鈥淚f a couple is considering the woman鈥檚 age in terms of when to have kids, they should probably worry about his to some degree as well.鈥�

But for couples experiencing fertility problems, there is little to be done if the cause of the issue lies with the man. 鈥淲e have no effective therapies to improve male fertility,鈥� says Pacey. 鈥淚f we did, that would be a game changer.鈥� Treatments for women include IVF, a range of hormone treatments to boost ovulation as well as surgical procedures; for men, there are few effective options.

This underlies a striking fact 鈥� that we understand surprisingly little about male fertility. Earlier this year, the World Health Organization described current knowledge of male infertility as 鈥渧ery low鈥�. The UK Medical Research Council has since issued a call for projects in need of funding.

鈥淭he major questions that we were asking 30 years ago about how male reproduction works we still don鈥檛 have any answers to,鈥� says Sharpe. 鈥淚t is a fundamental ignorance, and it hampers our ability to interpret data, and to manage an infertile male, because we have very, very little that we can offer.鈥� Doctors recommend that men make general healthy lifestyle changes, but little of this advice is evidence-based (see 鈥�Sperm-boosting lifestyle?鈥�).

And until men discover they have a fertility issue, they don鈥檛 want to consider it, says Pacey. 鈥淚 think men are mostly oblivious to their fertility and to the risks to their fertility.鈥� The evidence backs this up. Last year, the first large-scale survey that took place in Canada and found that men were only able to identify around half of the risk factors and health issues associated with male infertility.

Reframing the conversation about fertility to include men should help address this. It could also offer relief to those men who also feel a social pressure to have children by a certain age. This 鈥渟ocial clock鈥� is rarely talked about among men, which can be very hard for those struggling to start a family or who feel they haven鈥檛 met the right person in time, says Robin Hadley who studied involuntary childlessness in older men at Keele University, UK.

For all the men like my father who do become parents later in life, there are increasing numbers of couples who won鈥檛 be able to have the family they so desperately want. Until male infertility is taken as seriously as women鈥檚, that will only get worse. 鈥淲e think that we are the most advanced species on Earth, and now many couples are unable to conceive naturally. It鈥檚 unbelievable,鈥� says Levine. 鈥淚 hope that we can do something to pay more attention to male fertility, but the correct approach would be to look at the fertility of couples. It鈥檚 more complicated, but that鈥檚 life 鈥� and I鈥檓 optimistic that once we recognise the problem, we will find solutions.鈥�

This article appeared in print under the headline 鈥淚nconceivable truth鈥�