Men should start a family before the age of 35 to avoid health risks to their children, says a major study.
Researchers, who tracked 40million babies, found an increase in birth complications when fathers hit their mid-30s, and a sharper rise after the age of 45. For decades, women have been warned of risks to their children's health if they wait until they are older to give birth. The new study shows that the same applies to men.
Infants born to fathers aged 35 to 44 were 5% more likely to be born premature or have a low birth weight than those born to men aged 25 to 34.
With fathers aged 45 or older, there were 14% more babies who needed intensive care, 14% more born prematurely, 18% more who suffered seizures and 14% more with a low birth weight. If a father was 50 or more, 28% more infants needed intensive care and 10% more newborns had to be put on ventilators. Professor Michael Eisenberg, of Stanford University School of Medicine in the US, said: "This study shows that having a healthy baby is a team sport and the father's age contributes to the baby's health too. 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."
The report, published in the British Medical Journal, says the risk factor increases because with every year that a man ages, he acquires two new mutations to the DNA of his sperm.
Previous studies show that women with older male partners also take longer to conceive and are more likely to miscarry.
But Professor Eisenberg said the absolute risks were still relatively low.