As a field, there are two common questions when it comes to studying the implications of men trying to conceive as they grow older.
The first question is whether it becomes harder for that man to father a child. The answer appears to be yes, though at later ages than when it becomes problematic for a woman.
The second question is whether offspring of older men are any different than those of younger men. The answer appears to be yes. For the moment, this is most concentrated around the development of psychosocial disorders, but it’s important to remember that the absolute risk is still low.
While women are born with a finite number of eggs, which helps explain the drop-off in fertility in a woman’s 30’s and 40’s, men continually produce new sperm. This is why the impact of age on male infertility is more gradual and, frankly, harder to characterize.
Around a man’s mid-40’s age seems to become a factor. Below is a study looking at the length of time required to conceive for couples, broken down by the man’s age. As you can see, the amount of time rises sharply around age 45. The data comes from a study in the UK of over 2,000 births and the results were statistically significant.
Many studies plotting male age against their ability to conceive are unhelpful because the investigators don’t isolate out the fact that older men tend to have older female partners. This study isolates out those variables. To further adjust for the female-age confounder, the study’s investigators looked solely at the data for men who had partners under the age of 25. The cohort of men over the age of 35 are clearly negatively impacted.
There is good reason to believe that an older man’s challenges in conceiving can be counterbalanced if his female partner has especially good fertility.
To this point we’ve shown that older men require a longer time to conception. After conception, the risk of miscarriage remains relatively flat until the man enters his 50’s.
As always, we’re left to wonder how this impacts couples going through IVF. Said differently, can IVF help older men overcome the challenges of age to conceive. Frankly, the data is divided. We’ve seen compelling studies that both prove and disprove that paternal age plays a role in IVF success rates.
At what age does it become ill-advised for a man to reproduce for fear it will impact the health of his offspring? The truth is, that’s still hard to say. It's still uncommon for men to father children after, say, the age of 50 (only 1% of births), and the downstream conditions linked to genetic anomalies (for instance, autism) are still relatively rare, so we need much larger datasets to derive strong insight. That said, here’s what we know, or think we know.
The study we like best on this topic is a 2007 Kaiser Permanente review of the 150,000+ births in their system. The team did a nice job disaggregating a lot of variables and came to the conclusion that children born to fathers over age 40 had an 0.8% – 0.9% chance of developing Autism, up from around 0.2 – 0.5% for children born to men in younger age brackets.
Likely the best study on the impacts of a father’s age on children’s bipolar disorder comes from Sweden. Investigators looked at over 7 million births and over 14,000 cases of bipolar disorder. Ultimately investigators came to conclude that paternal age carries a gradual increased risk for bipolar disorder and that when paternal ages reach 55, there is a 37% increased relative risk. Since 1 in 100 Americans are diagnosed with Bipolar Disorder, the overall risk is likely below 2 in 100.