Parental age is rising around the globe. Here in the U.S., maternal age increased from about 24.6 years in 1970 to around 26.3 by 2014.^{1, 2} While birth certificates are collected at the maternal level, data on paternal age are also queried from the mother. Using those data, investigators have shown that paternal age has also increased in the U.S. over the past several decades.³ In the early 1970s, the average age of the father was 27.4, while it increased to 30.9 in 2015. This increase is seen across all races/ethnicities, levels of educational attainment and regions in the U.S.

While the definition of advanced paternal age is hard to precisely define, the numbers of births to fathers over thresholds offered by several organizations (including the recent American Urological Association/American Society for Reproductive Medicine Male Infertility Guidelines) are increasing.^4,5 Indeed, percentages of births to fathers over the age of 40, 45 and 50 now represent 0.9%, 2.9% and 8.9% of all births in the U.S., respectively, compared to half those rates 40 years ago.³ As we see these demographic shifts, investigators have examined the reproductive consequences.

While the oldest father ever is 96, studies have shown that changes can occur in a man’s fertility as he ages. Examining data from 90 studies including over 90,000 men, Johnson et al reported that semen volume, sperm concentration, total sperm count, morphology, total motility and progressive motility all decline with increasing male age.⁶ In addition, DNA fragmentation showed a positive association with paternal age. Moreover, investigators have identified longer times to pregnancy among couples with older male partners.⁷

Paternal age has also been associated with pregnancy-associated complications, including pregnancy loss, birth defects, preterm birth, low birthweight, low APGAR score and time in the neonatal intensive care unit (NICU).⁸ Interestingly, paternal age has also been associated with maternal pregnancy complications such as gestational diabetes.

As spermatogenesis continues throughout a man’s life, the chance of transmissible mutations can increase. Investigators report a consistent additional mutation load in the DNA of sperm.⁹ In 1912, Wilhelm Weinberg reported an association between birth order and achondroplasia, which was later attributed to paternal age. Additional paternal age effect developmental disorders are now categorized from mutations in proliferation pathways that lead to a competitive advantage from the mutated germ cell lines, described as the “selfish spermatogonial selection.”¹⁰

In addition, certain childhood diseases and disorders are associated with paternal age. Studies have demonstrated higher risk of childhood cancers (eg central nervous system tumors, leukemia) and adult cancers (eg breast and prostate cancer) in children of older men.¹¹ Proposed mechanisms include increased DNA damage, increased de novo mutations and aberrant epigenetic regulation among older men.

Neurodevelopmental outcomes have also been studied. Paternal age has been associated with autism, schizophrenia, psychosis and bipolar disorder.¹² In addition, academic achievement of children is associated with paternal age.

In summary, paternal age is rising in the U.S. with relevance not only to the reproductive health of the man, but also the coming generations.