On older parenthood

Fabulous article in TNR about the myriad implications of older parenthood.  Not just the implications for older parents themselves, but the sociological and medical implications for society as well.  Truly fascinating.  I find the subject particularly interesting given the age spread of my children.  While not exactly a young parent for David– I was 27,  that’s certainly on the younger side for my socio-economic stratum– I’m definitely on the older side for Sarah, being 38 when she was born.  I see the much younger parents when I drop off Sarah at pre-school and think, “that was me with David a decade ago.”  Anyway, some of the more interest bits.  First, the numbers:

American first-time mothers have aged about four years since 1970—as of 2010, they were 25.4 as opposed to 21.5. That average, of course, obscures a lot of regional, ethnic, and educational variation. The average new mother from Massachusetts, for instance, was 28; the Mississippian was 22.9. The Asian American first-time mother was 29.1; the African American 23.1. A college-educated woman had a better than one-in-three chance of having her first child at 30 or older; the odds that a woman with less education would wait that long were no better than one in ten.

It badly misstates the phenomenon to associate it only with women: Fathers have been getting older at the same rate as mothers. First-time fathers have been about three years older than first-time mothers for several decades, and they still are. The average American man is between 27 and 28 when he becomes a father. Meanwhile, as the U.S. birth rate slumps due to the recession, only men and women over 40 have kept having more babies than they did in the past.

Among the most profound implications is that older parents are at significantly more risk for children with all sorts of disabilities (not just the well-known Downs Syndrome link):

Soon, I learned that medical researchers, sociologists, and demographers were more worried about the proliferation of older parents than my friends and I were. They talked to me at length about a vicious cycle of declining fertility, especially in the industrialized world, and also about the damage caused by assisted-reproductive technologies (ART) that are commonly used on people past their peak childbearing years. This past May, anarticle in the New England Journal of Medicine found that 8.3 percent of children born with the help of ART had defects, whereas, of those born without it, only 5.8 percent had defects.

A phrase I heard repeatedly during these conversations was “natural experiment.” As in, we’re conducting a vast empirical study upon an unthinkably large population: all the babies conceived by older parents, plus those parents, plus their grandparents, who after all have to wait a lot longer than they used to for grandchildren…

The risk that a pregnancy will yield a trisomy rises from 2–3 percent when a woman is in her twenties to 30 percent when a woman is in her forties.

In the scientists’ study, published in Nature, they concluded that the number of genetic mutations that can be acquired from a father increases by two every year of his life, and doubles every 16, so that a 36-year-old man is twice as likely as a 20-year-old to bequeath de novo mutations to his children.

The Nature study ended by saying that the greater number of older dads could help to explain the 78 percent rise in autism cases over the past decade.  Researchers have suspected links between autism and parental age for years. One much-cited study from 2006 argued that the risk of bearing an autistic child jumps from six in 10,000 before a man reaches 30 to 32 in 10,000 when he’s 40—a more than fivefold increase.

Of course, my reproductive cycle is an N of 1, but I do find it mildly ironic that my later two kids are so far pretty much perfect (normal extreme whininess, etc., aside) whereas my first two kids include one with ADHD and mild/moderate sensory integration issues and another one with a full-blown rare genetic disease.

The article continues to have a fascinating discussion of epigenetics, something I’ve only half-understood, and looks at how it may be really key in these issues:

To the danger of age-related genetic mutations, geneticists are starting to add the danger of age-related epigenetic mutations—that is, changes in the way genes in sperm express themselves. Epigenetics, a newish branch of genetics, studies how molecules latch onto genes or unhitch from them, directing many of the body’s crucial activities. The single most important process orchestrated by epigenetic notations is the stupendously complex unfurling of the fetus. This extra-genetic music is written, in part, by life itself. Epigenetically influenced traits, such as mental functioning and body size, are affected by the food we eat, the cigarettes we smoke, the toxins we ingest—and, of course, our age. Sociologists have devoted many man-hours to demonstrating that older parents are richer, smarter, and more loving, on the whole, than younger ones. And yet the tragic irony of epigenetics is that the same wised-up, more mature parents have had longer to absorb air-borne pollution, endocrine disruptors, pesticides, and herbicides. They may have endured more stress, be it from poverty or overwork or lack of social status. All those assaults on the cells that make sperm DNA can add epimutations to regular mutations.

Okay, I could go on and on, but one last little bit that really intrigued me:

Another popular procedure coming under renewed scrutiny is ICSI (intracytoplasmic sperm injection). In ICSI, sperm or a part of a sperm is injected directly into an extracted egg. In the early ’90s, when doctors first started using ICSI, they added it to in vitro fertilization only when men had low sperm counts, but today doctors perform ICSI almost routinely—procedures more than doubled between 1999 and 2008. And yet, ICSI shows up in the studies as having higher rates of birth defects than any other popular fertility procedure. Among other possible reasons, ICSI allows sperm to bypass a crucial step in the fertilization of the egg—the binding of the head of the sperm with the coat of the egg. Forcing the sperm to penetrate the coat may be nature’s way of maintaining quality control.

Huh.  Short version– nature really knows what it’s doing.

Anyway, lots more good stuff about the social implications and the cost/benefit of being older, more stable parents versus being younger and less secure but also much less likely to have kids with a disability.  And, a part that really hit home about being an older parent of a child with a disability and wondering who is going to take care of that child some day.   For this, I’m really glad Alex has three siblings who are all incredibly exasperated by him at times, but also all love him dearly.

Okay, long post.  Just find some time to read the article.

About Steve Greene
Professor of Political Science at NC State http://faculty.chass.ncsu.edu/shgreene

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