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Parenthood spreads through social networks like a technological innovation, fashion trend, or a nasty virus. Although half of all births in the US are unplanned, individual and couple-level fertility decisions—including timing, parity, and voluntary childlessness—are strongly influenced by the fertility of one's social network members (Bernardi and Klarner 2013; Lois and Becker 2014). And one's "risk" of giving birth increases significantly after a sibling, friend, acquaintance, or coworker has a child (Kotte and Ludwig 2012; Lois and Becker 2014; Lyngstad and Prskawetz 2010; Pink, Leopold, and Engelhardt 2014).

In other words, childbirth is contagious. So how do prospective parents catch it?

Individuals and couples do experience substantial social pressure to become parents, and this pressure appears to be intensified when a social network member has a child (Bernardi 2003; Lois and Becker 2014). When I was first married, I was shocked by how many people asked me when I was going to have a child. We know that pronatalist pressure is commonly exerted by prospective grandparents (Bernardi 2003), but new parents also pressure their childless friends to take the plunge (Lois and Becker 2014). When one’s friends and siblings transition to parenthood, it may create or reinforce local social norms about the value of children and the appropriate timing of parenthood. Indeed, normative pressure is a strong predictor of first births (Udry 1982) and the pronatalist impact of a birth in a woman’s social network has a larger impact when the new and prospective mothers are of a similar age (Pink, Leopold, and Engelhardt 2014).

Parenthood might also spread through a social learning process. When a social network member has a child, childless individuals and couples are able to learn about the joys and challenges of parenthood (Lois and Becker 2014; Pink, Leopold, and Engelhardt 2014). The more parents there are in a given individual or couple’s social network, the more positive their experiences with children tend to be (Lois and Becker 2014). In turn, these positive attitudes toward children increase the couple’s odds of becoming parents (Lois and Becker 2014). Social learning may also be in part an unconscious process of emotional contagion: Contact with friends’ and siblings’ babies may trigger an emotional response among some childless adults, spurring a desire for their own children. It may help them decide the time is right for the children they always intended to have eventually (Bernardi 2003; Lois and Becker 2014).

Finally, the greater the number of social network members who become parents, the lower the perceived social opportunity costs of parenthood (Lois and Becker 2014). That is, most prospective parents anticipate losing social ties to non-parents; this loss of social ties would be greater the fewer other parents there are in the network. (If social ties between parents and non-parents were extremely fragile, prospective parents would never have many parents in their network. This suggests that prospective parents may overestimate the number of non-parent friends that they would lose by becoming parents.)

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Inversely, these processes suggest that current below-replacement fertility rates in many developed nations might be self-reinforcing (Lois and Becker 2014; Lutz, Skirbekk, and Testa 2006). As the number of parents in a given area declines, so too do many of the social processes encouraging childbearing.

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Bernardi, Laura. 2003. "Channels of Social Influence on Reproduction." Population Research and Policy Review 22:527-555.

Bernardi, Laura and Andreas Klarner. 2013. "Social Networks and Fertility." Demographic Research 30:641-669.

Guttmacher Institute. 2015. "Unintended Pregnancy in the United States."

Kotte, M. and V. Ludwig. 2012. "Intergenerational Transmission of Fertility Intentions and Behavior in Germany: The Role of Contagion." Vienna Yearbook of Population Research 9:207-226.

Lois, Daniel and Oliver Arranz Becker. 2014. "Is Fertility Contagious? Using Panel Data to Disentagle Mechanisms of Social Network Infleuences on Fertiltiy Decisions." Advances in Life Course Research 21:123-134.

Lutz, W., V. Skirbekk, and M.R. Testa. 2006. "The Low-Fertility Trap Hypothesis: Forces That May Lead to Further Postponement and Fewer Births in Europe." Vienna Yearbook of Population Research:167-192.

Lyngstad, Torkild Hovde and Alexia Prskawetz. 2010. "Do Siblings' Fertility Decisions Influence Each Other?" Demography 47:923-934.

Pink, Sebastian, Thomas Leopold, and Henriette Engelhardt. 2014. "Fertility and Social Interaction at the Workplace: Does Childbearing Spread Among Colleagues?" Advances in Life Course Research 21:113-122.

Udry, J. Richard. 1982. "The Effect of Normative Pressures on Fertility." Population and Environment 5:109-122.

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