Paternal Age and Fertility
Advanced paternal age is generally defined as a father > 40 years of age. Sperm banks that sell donated sperm typically do not accept donors over the age of 50 years. It’s well known that as men get older, their fertility declines, but at a later age, and to a lesser degree, than women. Here’s what happens to fertility as men age:
- Testosterone levels fall about 1% per year after age 40.
- Daily sperm production remains relatively constant.
- Sperm motility falls about 7% per year.
- Ejaculate volume falls with age.
- DNA damage, a measure of sperm “robustness,” increases with age.
The effects of these changes on fertility are hard to assess since erectile dysfunction, decreasing frequency of intercourse and partner’s maternal age can also affect fertility as men age.
Paternal Age and Sperm
As men age, the quality control processes during sperm production are taxed, often heavily, since 1000 sperm are produced per heartbeart in normal men. Because of this, genetic alterations occur more frequently in sperm as men age:
- Sperm chromosomal abnormalities increase, especially among the sex chromosomes X and Y, which can be transmitted to offspring.
- Single gene mutations occur in sperm DNA. This causes a handful of rare but debilitating diseases in offspring (Table 1).
Paternal Age and Pregnancy Outcomes
Even after successful conception, paternal age has been linked to other pregnancy issues:
- Spontaneous miscarriage rates are twice as common in partners of men age 50 years or older.
- Early births (< 32 weeks) and fetal deaths are twice as high in older compared to younger fathers.
So, even after “fertility” is achieved, male partner age can influence the eventual success of pregnancies.
Paternal Age and Birth Defects and Diseases in Offspring
In addition to the single gene disorders in offspring (Table 1), various other complex disorders and birth defects have also been linked to paternal age (Table 2) with an overall estimated increased risk of 20% as men age.
Importantly, there is now solid evidence that being an older father leads to an increase in several adult diseases in offspring. These cognitive disorders include schizophrenia (5 fold higher), autism (4 fold higher), bipolar disorder (2 fold higher) and the spectrum of attention deficit disorders (ADHD, 2 fold higher) and are listed in Table 3.
What Should You Do?
Based on current, developing knowledge, men should understand that they too have a “biological clock” and proceed to become fathers with caution. Still, yiou should know that the overall risk is still quite low. And, currently, there is no testing to assess the risk beforehand. For concerned individuals, the pregnancy should be treated like a “high-risk” pregnancy, and the mother should have the appropriate prenatal screenings and tests that women receive for a high-risk pregnancy.
Table 1. Single gene disorders in offspring linked to paternal age.
Table 2. Birth defects in offspring associated with advanced paternal age.
Table 3. Cognitive disorders in offspring associated with advanced paternal age.