Are We Less Fertile Today?

How big was your family a couple of generations ago? Dial things back a half a century and you’d see that having three or four kids was pretty much average in America. Now, having two or fewer kids is the norm. What happened? Are we less fertile?

I know what you’re thinking: So what if modern families are smaller? What with urbanization, industrialization, and vastly different socioeconomics, family size had to change too, right? To boot, couples now marry later (if at all) and use much better contraceptives to control their busy, engaged, and productive lives. Makes perfect sense.

Human Capital
But what if it’s not that simple? Could our sleepless and stress-filled lifestyles, our haphazard diets, and rambunctious social habits be making us less fertile? Might the 87,000 known chemicals, endocrine disruptors, and just plain old pollution hovering over our post-industrial environment finally be rearing their ugly heads and affecting reproduction? And exactly what risk does this pose for future generations?

Governments have a strong interest in having a sustainable population, and that’s in part why the Feds asked us to meet this week in Washington. Approximately 50 great minds from all over the globe were sequestered in a room for two days to address one simple question: Is Human Fecundity Changing?

Slice and Dice
As a surgeon, I am a big fan of dichotomous answers. Gather information to answer a simple question: to cut or not to cut. It makes life much simpler. But the truth here is that the answers are entirely unknown. Moreover, any information we do discover will certainly not be quite so cut and dry.

Here are some of the startling conclusions that I took away from this intriguing think tank:

• Infertility affects an estimated 15% of couples in the U.S. and globally, and it is not at all clear that this rate has changed over time.
• Definitions matter. “Fertility rate” reflects sheer birth numbers, while  “fecundity” refers to the innate capacity to reproduce. As experts, we agreed that changes to fecundity are more worrisome but are also harder to measure.
• Much of human infertility may actually be “social” and not biological in origin. Jobs, disasters, wars, divorce, etc. comprise the messy aspects of life that can heavily influence reproductive behavior.
• As a corollary, the several-decade-trend toward later “unions” causing delayed reproductive “coupling” decreases critical baby making “exposure time” and might be significantly influencing human fecundity.
• Environmental impacts on human fertility are incredibly difficult to assess, something akin to finding small needles in large haystacks.
• Using math to model sexual behavior, however inhuman that sounds, could provide clues about temporal trends in infertility, particularly among advanced parental age couples.
• We need a better biomarker than the simple, unruly and widely variable semen analysis to help us assess changes in male fecundity.

Where Things Stand

In the eight years since this summit, experts like me have continued to monitor these topics. Recently, multiple studies have pointed to air pollution’s negative effects on male and female fecundity, which may warrant more consideration from the federal government pending more research. While there is no indication that fecundity rates have shifted significantly during this span, it is wise for the government to keep track of any emerging trends to formulate a response if necessary.

Ever the optimist, I believe that we are still the simple and reproductively capable cavepersons we once were, only mildly diverted by our bigger brains that have led us to think a little too much and too often. Given the serious intellectual firepower and interest that is now being dedicated to this issue, I am certain that elemental truths will usher forth on this hot and steamy topic with time.