A study tracking 40million babies found the risk of birth complications start to increase when fathers are in their mid-30s, and significantly rise from the age of 45.
For decades women have been told they will put their children at risk if they pursue a career first and leave it until they are older to have a family.
But the new study, published in the British Medical Journal, shows men should also take responsibility.
Researcher Professor Michael Eisenberg, of Stanford University School of Medicine, said: ‘We tend to look at maternal factors in evaluating associated birth risks.
‘But this study shows that having a healthy baby is a team sport, and the father’s age contributes to the baby’s health, too.’
He said once a father hits 35, there’s a slight increase in birth defects, but the risk increases more sharply as men age into their 40s and 50s.
This is because with every year that a man ages, he accumulates on two new mutations in the DNA of his sperm.
Compared with fathers between the ages of 25 and 34, infants born to men between the age of 35 and 44 were about five per cent more likely to be born premature or of low birth weight.
For men aged 45 or older they were 14 per cent more likely to be admitted to intensive care, 14 per cent more likely to be born prematurely, 18 per cent more likely to have seizures and 14 per cent more likely to have a low birth weight.
If a father was 50 or older, the likelihood that their infant would need ventilation upon birth increased by 10 per cent, and the odds that they would require intensive care increased by 28 per cent.
Professor Eisenberg added: ‘What was really surprising was that there seemed to be an association between advanced paternal age and the chance that the mother would develop diabetes during pregnancy.’
For men age 45 and older, their partners were 28 per cent more likely to develop gestational diabetes, compared with fathers between 25 and 34.
He said the possible biological mechanisms at play on this point are unclear, but he suspects that the mother’s placenta has a role.
Some 18 per cent of children born in England and Wales have a father aged 40 and above, according to the Office of National Statistics.
The average age of fathers in 2016 was 33.3, nearly four years older than 1974, when they were 29.4.
The age of mothers have increased at almost exactly the same rate – they had an average age of 30.4 in 2016, and 26.4 in 1974, also a rise of four years. But Professor Eisenberg said the absolute risks are still relatively low.
The absolute risks are still relatively low
He compared the increased risks to buying lottery tickets. ‘If you buy two lottery tickets instead of one, your chances of winning double, so it’s increased by 100 per cent,’ he said.
‘But that’s a relative increase. Because your chance of winning the lottery started very small, it’s still unlikely that you’re going to win the lottery. This is a very extreme example, but the same concept can be applied to how you think about these birth risks.’ The researchers wrote: ‘
A significant number of these negative birth outcomes were estimated to be prevented if older fathers had elected to have children before the age of 45 years.
‘The risks associated with advancing paternal age should be included in discussions regarding family planning and reproductive counselling.’
More mothers are waiting until later in life to have children, but pregnancy after 50 is still quite rare.
A woman’s fertility begins to decline in her early 30s. After age 35, her number of viable eggs starts to fall more quickly.
Women are born with a set amount of follicles – between one and two million – or immature eggs.
These develop at different rates. Some follicles never release an fully-fledged egg, but each month the ovaries release one egg to wait for fertilization in the uterus.
Most women only ovulate around 450 eggs over the course of their lives, so by their late 40s, most have run out and start to head toward menopause.
Menopause begins around age 51 for the average woman, at which point pregnancy becomes impossible.
However, even as fertility is declining among American women (and men) overall, one group is having a few more babies than they did in the past: older women.
The birthrate among women between 45 and 49 – the oldest group that the Centers for Disease Control and Prevention tracks – went up by 0.1 percent between 2016 and 2017.
In 2013, an estimated 677 American women over 50 gave birth, marking a 370 percent increase over the 144 such births in 1977.
So far, an Indian woman believed to be in her 70s who had a baby boy in 2016 is thought to be the oldest to give birth, though a 66-year-old holds the official record.
Celebrities too, have made headlines for having in their later years, including Janet Jackson who had her son, Eissa Al Mana, at age 50.
A growing number of women choose to freeze their eggs – which decline in quality with age – while they are younger, use IVF, surrogates or donor eggs in order to have children at more advanced ages.
But pregnancy after peak fertility can come with risks.
Older women are more likely to develop high blood pressure, preeclampsia, diabetes and heart problems, so most doctors screen them carefully if they are trying to conceive.
If women in this age group do get pregnant, doctors will continue to monitor them closely as a precaution, but they can certainly have healthy pregnancies, and a growing number are doing just that.