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Monday
Mar022015

Catching Fertility

As a 40-something, married father of two, I’ve experienced a lot of transitions in my life, including some particularly big ones over the past decade or so. I started a new job, got married, had a kid, bought a house, and had another kid. Importantly, I’m not unique in this regard --- many of the people I know my age have gone through most, if not all, of these same transitions (albeit perhaps in a different order).

Although I didn’t really notice it at the time, my movement through these life transitions generally occurred in the ballpark of my friends doing the same things. How can I forget the ‘wedding years’, when I was finally forced to buy a suit. And then there was the breeding extravaganza that happened a few years later. Is it a coincidence that many of my friends also have kids within a few years age of my own? Perhaps not.  In fact, it’s very likely that the decisions my wife and I made about starting a family were influenced by what we saw going on around us.

Simply put, others influence our thoughts about fertility. For example, adolescents are more likely to become sexually active, and make choices about whether to do so and take appropriate precautions, if their friends are doing the same (You don’t use condoms? Then me neither! Let’s compare babies and rashes!). In a recent study, researchers wanted to see just how far a reach friends have on women’s sexual and fertility behaviors by testing whether female friends’ transitions to parenthood increase a given woman’s own transition to parenthood. Put another way: Is a woman’s fertility contagious?

Why or how could this happen? The researchers drew on three basic ideas regarding the link between others’ behaviors and our own.

  1. Social Influence: Basically, we look around to the people who are similar to us (i.e., our friends) and use their behaviors and decisions to develop our own thoughts about what’s typical or normal. So, if you’re on the fence about having kids but a few of your good friends all suddenly stop drinking on girls’ night out, you might decide to get off that fence in a hurry.
  2. Social Learning: The thought of becoming a parent can be intimidating if not terrifying (to be fair, being a parent IS often terrifying!). What’s going to happen to my relationship (if I’m in one)? What about my body? Am I ever going to survive all the lost hours of sleep? You get it. But when we see people around us go through the transition, the curtain gets pulled back and what was once intimidating may start to feel much less so as we learn from others’ experiences and develop a better idea of what to expect.
  3. Pragmatics: There are some very pragmatic benefits to jumping on the breeding bandwagon. For example, the transition to parenthood is often isolating and is always costly. Having others to share the experience with, trade tips, share costs (e.g., hand-me-downs), hang out on play-dates, and so on are all reasonable benefits to procreating en masse with others. Because of all of these forces, for lack of a better term, and particularly because of the rational benefits noted above, the researchers expected that if women do catch fertility, they would typically do so fairly soon after their own friends become pregnant or have children (as a large age gap between kids would cut back on many of the benefits). 

To test their hypothesis, the researchers used data from a large-scale study called Add Health (we’ve written about the study before) in which individuals completed several sets of measures beginning around age 15 and going through age 30ish. The researchers analyzed a subsample of 1726 women who provided lists of their friends at several points in time, allowing the researchers to identify females’ friends who were also in the study (and provided fertility data). Because the women provided the lists at several points, the researchers were able to determine with whom the women remained friends with during and beyond high school (i.e., close friends) vs. those that dropped out of their social circles after high school (i.e., peers, or friends somebody loses touch with).

Over the course of the study, 820 of the women had a child, with the typical age at first birth at just over 27 years. How did those births affect the likelihood of pregnancy and childbirth for those women connected to those who had a kid? As expected, it increased the ‘risk’ (the researchers’ term, which is a statistical term but one that I find humorous in this context). Specifically, if a given woman’s close friend(s) had a kid, that woman was more likely to have a child within a couple of years as well. In contrast, (non-close) peers did not show the same influence on women’s childbearing.*

Importantly, and interestingly, the contagiousness of childbirth only shows up for intended pregnancies; no matter how few of your friends aren’t having kids, you are not inoculated against getting pregnant unless you take appropriate precautions. Put another way, if you are sexually active and aren’t consistently and correctly using reliable birth control, no amount of non-parents in your immediate social circle will keep you from getting pregnant.

In many respects, this phenomenon is similar to the conceptually similar ‘pressure’ implied by the phrase “always a bridesmaid, never a bride”. I’ve never heard the parallel “always a godmother, never a mother”, but this analysis highlights yet another way our social environments profoundly influence what happens in our lives. And it also means your own decision to have a child may make you ground zero for a pregnancy outbreak of your own.

*Of course, the possibility remains that women choose to remain friends with other women who share their attitudes about fertility, childbearing, and the like (i.e., it’s not a causal influence, per se, but rather a result of the fact that people tend to be and remain friends with similar others). On the surface, this is certainly a logical counter-explanation. But you’ll have to trust me that the researchers covered their bases and accounted for any possible selection effects as best as is possible both statistically and theoretically. Exactly how they did so, however, is quite nuanced and beyond the scope of this summary.

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Balbo, N., & Barban, N. (2014). Does fertility behavior spread among friends? American Sociological Review, 79, 412-431.

Dr. Tim Loving - Science of Relationships articles | Website/CV
Dr. Loving's research addresses the mental and physical health impact of relationship transitions (e.g., falling in love, breaking up) and the role friends and family serve as we adapt to these transitions. He's a former Associate Editor of Personal Relationships and his research has been funded by the National Institute of Child Health and Human Development.

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Reader Comments (2)

Did you mean to say "Always a bridesmaid, never a bride"?

March 2, 2015 | Unregistered CommenterHerb

Thanks, Herb. Our mistake. The wording has been fixed.

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