For men who are reluctant to start a family, it is an age-old defence: there is no need to rush into fatherhood, as Des O’Connor, Luciano Pavarotti and countless rock stars have proved when they had children well after they qualified for their bus passes.

But men, just like women, can wait too long, doctors warn. A new study reveals that a couple’s chances of having a baby fall with the man’s age, to the point that it can have a substantial impact on their ability to start a family.

Laura Dodge, who led the research at the Beth Israel Deaconess Medical Center and Harvard Medical School in Boston, said that couples should bear the findings in mind when planning a family. “When making this decision, they should also be considering the man’s age,” she said.

Scientists have long known that a woman’s chances of conceiving naturally drop sharply from the age of 35, but fertility research has focused so much on women that male factors are less well understood. “The impact of age seems to focus almost exclusively on the female partner’s biological clock,” Dodge said.

To investigate the impact of a man’s age on a couple’s chances of having a baby, Dodge and her colleagues studied records of nearly 19,000 IVF treatment cycles in the Boston area between 2000 and 2014. The women were divided into four age bands: those under 30, 30-35 year-olds, 35-40 year-olds, and those aged 40-42. The men were divided into the same age brackets with an extra band for the over 42s. Some of the couples had received up to six cycles of IVF.

Dodge then looked at how age affected couples’ chances of having a live birth. As expected, women in the 40-42 age bracket had the lowest birth rates, and for these women the male partner’s age had no impact.

But for younger women the man’s age mattered. Women aged under 30 with a male partner aged 30 to 35 had a 73% chance of a live birth after IVF. But that impressive success rate fell to 46% when the man was aged 40 to 42. Whether they can hear it or not, the biological clock ticks for men too.

The study, to be reported at the European Society of Human Reproduction and Embryology meeting in Geneva on Tuesday, found that male age had no real impact on birth rate when his partner was the same age. But some women did benefit from being with younger men. When women aged 35-40 partnered with men aged 30-35, their chances of having a baby stood at 54%, a figure that rose to 70% when the man was under 30. On average, women aged 30 to 35 who had older male partners had live birth rates of 64% compared with 70% if the man was in the same age bracket.

“The value of this is not only in counselling couples,” said Nick Macklon, professor of obstetrics and gynaecology at the University of Southampton, who was not involved in the study. “It may help women to encourage their male partners to get a move on. We know from a number of studies that one of the reasons why women are having babies later is because men are sometimes slow to support the idea.

“This reminds us that it takes two to tango and it’s not just down to the age of the woman.” The research comes a year after scientists at the University of Copenhagen found that children born to older fathers had a greater risk of developing autism.

Researchers are not entirely sure why male fertility decreases with age. Women are born with their life’s store of eggs which accumulate mutations as they age. As a result, the overwhelming cause of infertility in older women is a rise in abnormal chromosomes in their eggs. In men, the ageing process affects sperm quality, making it harder to achieve a pregnancy and increasing the risk of miscarriage.

“Declining sperm quality certainly plays some role, but our work shows that this is not the whole picture,” Dodge said. “We found similar results among couples with no documented male infertility, so something else is happening.” Even though men produce fresh sperm every day, the cells the sperm are made from gather their own mutations, and older sperm carries more DNA damage. Dodge now plans more studies to investigate the causes.

“This is something we’ve suspected is the case, that male age probably has an effect on the success rate of fertility treatment,” said Raj Mathur, clinical lead for reproductive medicine at Manchester Fertility. “It is important and perhaps clinicians should start, when they are counselling couples, to take into account the age of the man as well.” He added that scientists should now study data held by the UK fertility regulator, the Human Fertilisation and Embryology Authority, to confirm the effect in a larger number of people. “It would answer this question more definitively,” he said.