乌鸦传媒

Age of new fathers in the U.S. has been rising steadily over the past 45 years for all regions, races, and education levels, researchers said -- just as has been the case for mothers.

Analysis of more than 150,000,000 births from 1972 to 2015 found that mean paternal age has increased 3.5 years (from 27.4 to 30.9), reported Yash S. Khandwala, of Stanford University School of Medicine, and colleagues.

Additionally, the percentages of fathers of newborns who were older than 40 increased from 4.1% to 8.9%; the proportion older than 50 also rose, from 0.5% to 0.9%, Khandwala's team wrote online in .

Fellow author Michael L. Eisenberg, MD, also of Stanford University School of Medicine, told 乌鸦传媒 that the trend suggests certain implications, including a likely shrinkage in average family size.

He also noted higher risk of certain diseases in offspring associated with older paternal age -- including neuropsychiatric, malignant, and congenital conditions.

"As such, these trends may suggest that we should be seeing more of these occur in children over time. However, as men and women have children older and more secure in their careers, they likely have more resources to share with their children which should be beneficial," he said via email.

Khandwala and colleagues analyzed data on 168,867,480 live births collected through the National Vital Statistics System (NVSS) of the Centers for Disease Control and Prevention (CDC). Demographic variables -- such as age, race, education, and birth state -- were extracted for mothers and fathers for each birth, and racial categories were provided by the NVSS and based on how individuals self-identified.

While mean paternal age of all races and ethnicities increased substantially over the study period, Asians were the oldest while blacks and Hispanics were the youngest. Japanese fathers in particular had the largest increase in mean age: from 30.7 in 1972 to 36.3 in 2015.

Fathers with less than high school, high school, or college level education all displayed increases in mean paternal age over the study period. However, during 2011-2015, fathers with college degrees were considerably older than those with only a high school diploma (33.3 versus 29.2).

Paternal age also increased across all regions of the U.S., with the oldest fathers found in the Northeast.

The researchers also reported that the parental age difference -- defined as paternal age minus maternal age -- declined slightly (2.7 years older in 1972 versus 2.3 years older in 2015).

"While we have known this [increasing age trend] for mothers, this is the first study to show this for fathers," Eisenberg explained. "The reason is also not certain. However, the possible explanations are likely similar to that for maternal age such as improved and more common contraception, men and women choosing to delay starting a family until they are more settled in their career, etc."

The proportion of paternal data reporting on all birth certificates is currently at 88.4%, up from 85.5% in 1991. The rate of reporting from 1985 to 2015 varied by the mother's race and ethnicity -- white (90%–93%), black (58%–71%), and Chinese (96%–99%) -- with a notable increase in paternal reporting for births to black mothers of 63.9% in 1985 to 70.9% in 2015.

Eisenberg said it would be valuable to "improve paternal reporting rates which have remained relatively stagnant over the past 40 years." The paper cited as a limitation that birth certificates sometimes lack paternal data. The researchers used inverse probability weighting to reduce the impact of paternal reporting bias, but acknowledged that estimates may still be influenced by missing data in the NVSS.

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