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London: The birth rate is declining in all industrialised countries, and socio-economic factors and women's age are not solely to blame. Male reproductive health and environmental factors are also significant, says a new scientific review article.
Researchers from Denmark, the US and Finland studied a number of factors related to fertility, and one of the main conclusions of their study was that poor semen quality contributed to increases in infertility and the use of assisted reproductive technology, a University of Copenhagen statement said.
The researchers observed lower levels of testosterone in average men.
"I was surprised that we found such poor semen quality among young men aged 20 to 25. The average man had up to 90 percent of abnormal sperm. Normally, there would be so many sperms that a few abnormal ones would not affect fertility," said first author of the article, professor Niels E. Skakkebaek from the department of growth and reproduction at Rigshospitalet and the University of Copenhagen.
"However, it appears that we are at a tipping point in industrialised countries where poor semen quality is so widespread that we must suspect that it results in low pregnancy rates," Skakkebaek added.
Many of the male reproductive problems could be due to damage to the testes during embryonic development. While the reproductive problems could arise from genetic changes, "recent evidence suggests that most often they are related to environmental exposures of the fetal testes," the researcher team wrote.
"Since the disorders in male genitals have increased over a relatively short period of time, genetics alone cannot explain this development. There is no doubt that environmental factors are playing a role and that endocrine-disrupting chemicals, which have the same effect on animals, are under great suspicion," Skakkebaek said.
"The exposure that young people are subjected to today can determine not only their own, but also their children's, ability to procreate," the professor added.
According to Skakkebaek, the study has significant public health implications as there is much focus on the age of delivering women as the only biological factor behind the low birth rates in industrialised countries.
"Age does indeed play a role. However, we found in our analysis that the average age of a delivering woman in Denmark in 1901 was the same as today, suggesting that delayed childbearing alone cannot explain the current trends," he said.
More research in reproductive medicine needs to be done to understand and address the declining fertility rates, according to researchers.
The article was recently published in the American journal Physiological Reviews.