Scientists have found that after the age of 39, men's sperm begins to deteriorate at a slow rate and any partner, regardless of her age, has less chance of becoming pregnant.
The findings presented at the European Society of Human Reproduction and Embryology's annual conference in Tours, France shows that after the age of 39, men are 7 per cent less likely with each advancing year to help produce a perfect fertilised egg. If a poor-quality embryo results, the woman has a greater chance of miscarriage.
Many couples are having children later in life, and although most women are aware that their fertility declines after the age of 35, this is the first clinical evidence to show that male age has an effect on the chances of becoming pregnant.
"Fertility specialists have not considered that male age has an effect before," said Dr Orhan Bukulmez, assistant professor of Obstetrics and Gynaecology, at Hacettepe University, Ankara, Turkey, and author of the research.
Dr Bukulmez said that one possible explanation was that the sperm of older men carries more genetic mutations due to the many cell divisions that have resulted in its production.
A 20-year-old man produces sperm that had resulted from about 200 cell divisions, compared with 890 divisions that have taken place in the testes of a man aged 50.
"There has been some animal data to show that in mate coupling there is an effect on advanced male age decreasing the chances of successful pregnancy," he said.
Previous research, analysing the life span of members of European royal families, has shown that men who father children later in life are more likely to produce daughters who have a shorter life span. The effect did not extend to sons, nor to the daughters of older women, and scientists believed that the effect was linked to defects in the X chromosome which men pass on only to their daughters.
In Dr Bukulmez's study, scientists graded the embryo quality produced by 800 men and women who were undergoing fertility treatment. The men had low sperm counts of fewer than three million and were undergoing intracytoplasmic sperm injection, fertility treatment where a single sperm is injected into the egg.
All embryos produced were graded into four categories. The top-quality embryos had zero to 10 per cent fragmentation, and the worst embryos, grade four, had 50 per cent fragmentation.
The findings showed that the number of top-quality embryos produced was the most reliable way to predict a successful pregnancy.
The number of top-quality embryos, those with no fragmentation, was best predicted by male age, with the cut-off age being 39 years old.
"We have found a quick and reliable method of checking predicting-pregnancy outcomes and are conducting further work to investigate the detailed effects of male age," said Dr Bukulmez.Reuse content