It is well known that as a woman ages, her ability to have a child with her own eggs declines and eventually ceases altogether. What has not been well studied nor as widely discussed is the impact that paternal age has upon fertility. With a growing number of couples delaying marriage or remarrying, there are more men in their forties, fifties and sixties that are trying to father a child. In the USA, the birthrate of children to men between 35 and 54 years of age has gone up by over 30% between 1980 and 2000[g1] . There is evidence that this trend is continuing to rise.
Advanced paternal age has been associated with a higher risk miscarriage in at least one study. Other studies suggest that women with an older partner are at higher risk of pregnancy complications. But the data on the chance of actually conceiving is more difficult to interpret.
As men a man becomes older the volume of semen that he produces declines. We know also that the number of sperm producing cells and the production of testosterone decreases as well. We also know that the hormone signal from his brain to the sperm producing cells increases suggesting that they are less sensitive to this signal. But the factors that we typically evaluate to assess male fertility--sperm count, sperm motility and sperm shape (morphology)--do not predictably decline as a man reaches his 50’s or 60’s. So to answer the question of male fertility and aging, we get the most predictable information by looking at the results of IVF treatment.
When pregnancies are created through advanced reproductive techniques like IVF; we are able to directly observe the ability of sperm to fertilize an egg and then track how the embryo develops. Better still, we can then follow the outcome of those embryos in order to determine how well they implant and how often the result in the birth of a healthy baby. Recently, a review [g2] was published that tried to gather and quantify all of the studies published so far that could help answer this question. Here is what they found:
· Fertilization Rate—this is defined by the ability of a sperm to penetrate an egg and initiate embryo development. The existing studies do not show a decline in this critical step associated with aging in men.
· Embryo Development—is the critical stage that an egg must go through before it can implant into a woman's uterus. This is a process that typically takes place over 5-6 days. The first three days are not impacted by sperm quality and therefore are not impacted by the age of the male. Studies do suggest that there is a greater decline in embryo quality between day 3 and day 6 as men age suggesting that sperm quality may be impacted by age.
· Implantation Rate—this is determined by the positive pregnancy rate following embryo transfer. The data suggests that the implantation rate does decline with paternal age but this does not become a noticeable impact upon success until a man is older than 60 years of age.
· Birth Rate—the data on live birth rate is conflicted. Some studies show a lower birth rate after implantation as a man ages while others found no higher risk of miscarriage. Typically, such inconsistent results suggest that it is not strictly an age related phenomenon and may in fact be impacted by other factors.