The decline in male fertility is alarming, but the world has not woken up to the impending crisis and its longer-term economic and social consequences, a leading clinical scientist in this field has warned.
One in 20 young men now have sperm counts that are low enough to make it difficult to have children, said Professor Christopher Barratt, an expert on reproductive medicine at the University of Dundee in Scotland.
He said sperm counts have been declining steadily for the past 40 years and when coupled with a rise in male reproductive illnesses such as testicular cancer, the outlook is worrying.
At the same time, scientists have not been able to conclude what the specific reasons for the disturbing trend are.
"The reality is, we don't know. That's the truth of the matter but it's likely to be an environmental effect, the mix of different chemicals in different countries, different spaces, so some chemicals can react quite negatively," said Prof Barratt, who was director of the male fertility expert working group at the World Health Organisation (WHO).
He stressed that the perception that all is well in the world of male reproduction is "an illusion".
As sperm counts decline, the chances of achieving conception are also lower. This, together with the rising trend of couples having children later, sometimes past their prime reproductive ages, has led to family sizes being below population replacement levels in many places including Hong Kong, Singapore and the European Union.
The downward spiral is compounded by other factors such as later marriages, rising number of singles, preference for fewer or no children and higher divorce rates.
Singapore's population now stands at around 5.64 million while Hong Kong's is nearly 7.5 million.
Both cities face a rapidly ageing population and for them to replace their populations without immigration, women need to have an average of 2.1 babies.
But Singapore's total fertility rate has plummeted from 1.82 in 1980 to an eight-year low of 1.14 in 2018.
Hong Kong has been singled out as having one of the lowest fertility rates in the world. Provisional government data show that the total fertility rate in 2018 slid to 1.07 from 1.125 in 2017.
Not helping the situation is the lack of knowledge, data and diagnostic tools about male infertility and ways to treat it, Prof Barratt said.
The Scandinavian countries and Australia have extensive research on male reproductive health but in most parts of the world including Africa, Asia and South America, little is known.
This, in turn, means women have to undergo a more costly and invasive intervention to boost a couple's chances of having a baby.
"In a world in which we claim to be addressing inequalities between men and women, the fact that the female partner often has to bear the burden of male infertility is an infringement of basic human rights and dignity," Prof Barratt said.
He has called on societies to be more aware of the situation, which he describes as a crisis, and on people to take action to change this.
Discussions on critical issues in reproduction will be addressed over four days at the 9th Congress of the Asia Pacific Initiative on Reproduction (Aspire 2019) in Hong Kong from today. Some 1,600 scientists, doctors and nurses are expected to attend.