Until recently, it was thought that men could father perfectly healthy children at any age, and that the only true impediment to a baby was the ageing mother and her aged eggs.
Research is showing us that men's age actually impacts on outcomes in a much greater - and sometimes far more devastating - fashion than we previously understood, including increasing their children's risk of autism, diabetes, and later in life, breast cancer.
Global data from over 60 research teams on the health risks for children born to older fathers has uncovered some critical information that those contemplating older-age pregnancies and fatherhood should know.
Key findings of a collection of studies
Men aged over 35 have a 50 per cent lower chance of conceiving over a 12-month period than men aged 25 and under, even after taking into account the age of the would-be mother.
The risk of miscarriage and premature birth increases when the father is over 40. In a study of almost 24,000 pregnant women, pregnancies involving men aged 50 and over were twice as likely to end in a miscarriage compared to younger fathers.
Fathers aged 40 and over passed on an increased risk of breast cancer in their daughters by around 60 per cent - this is just one of five studies to find a link between advanced paternal age and breast cancer.
Children born to fathers over 40 have a 30 per cent increased risk of suffering epilepsy, a 37 per cent higher risk of Down's syndrome, a 14 per cent greater chance of childhood leukaemia, and a whopping 70 per cent greater likelihood of central nervous system cancers like brain tumours.
Children of fathers over 45 have a threefold increased risk of retinoblastoma, a rare eye cancer.
Older fathers are now understood to be at a higher risk of having children with autism and schizophrenia.
Achondroplasia, a common cause of dwarfism, is eight times more likely to appear in the offspring of men over 50.
An analysis of over 11,500 pregnancies obtained by artificial insemination using donor sperm had an increased risk of trisomy 21 (the most common form of Down's syndrome caused by an extra chromosome) with donors aged 38 or over.
Why does this happen?
There are a few possibilities, but the most obvious is genetics. Sperm is made from precursor cells, which have to divide every 16 days. This means that by the time a man is 70, those cells have divided 1,500 times. Each divide comes with its own risks of DNA mutations and genetic defects.
An Icelandic study found that children born to a 20-year-old man have 25 DNA mutations in their genes, which increases annually, eventually reaching 65 mutations for men at age 40.
Another reason may be that after age 60, sperm is affected by what's known as DNA defragmentation - normally, sperm is wound up tightly to prevent the strands of DNA from snapping off, but if the package breaks down, the DNA can be more easily damaged. This could increase the nonviable pregnancy rate for older fathers.
Additionally, sperm quality drops with lower testosterone levels, which decrease as men age.
Why doesn't anyone know about this?
Because many of these impacts happen later in a child's life, it wouldn't really occur to anyone to look at paternal age as a factor, while other difficulties are more easily linked to the child's time in the womb, and up until recently, everyone was a far bit younger.
The research into male fertility outcomes is recent, with age becoming more and more relevant as time goes by. Childbearing later in life is now common, with the age at first birth getting later and later for more and more women. This means their partners are also getting older, and more babies are being born with blippy genetics.
What does this mean for insurers?
Genetic risk can now be established with greater certainty based on how old ones parents were when they were conceived, since the risks for an older father are often functionally different to those of women, and clearly the risks are abundant chromosomally, particularly for certain cancers.