Pregnancy Is Contagious

"The study shows the contagion is particularly strong within a short window of time."

It starts slowly. A baby shows up on your Facebook feed. Your friends, like you, are getting older, settling down and starting families. Pretty soon, your entire newsfeed is flooded with tiny children covered in what was supposed to be their first experience with solid food, birthday parties, and all the small milestones of a child's development ("his first wink!").

It's an epidemic of cute, in which every one of your old high school friends seems to be having children around the same time. And new research says you're not crazy to think so.

Pregnancy is contagious. That's the conclusion of a study just published in the American Sociological Review; the decision to have a child is influenced by social networks stretching back to high school. "A friend's childbearing positively influences an individual's risk of becoming a parent," the study concludes, with a phrasing reminiscent of "friends don't let friends do drugs."

Furthermore, "an individual's risk of childbearing starts increasing after a friend's childbearing," reaching "a peak around two years later." Coauthor Nicoletta Balbo summed those results up like this in a press release: "The study shows the contagion is particularly strong within a short window of time." Like the flu.

Though this isn't about high school pregnancy pacts and teen moms. (Teen pregnancy rates are actually at their lowest in years.) This study looked at the effects of high school friends 15 years on, following 1,700 women tracked from the age of 15 to around 30. In the group, the median age for birth of the first child was 27.

The research also didn't find any link between high school friends and unintended pregnancies. The implication here is intuitive: Friends influence major life decisions.

"Having a child (or not) is the outcome of several interrelated decisions and behaviors, ranging from committing to a union, to having sex, using contraception, and having an abortion," the authors write. "Each action may be influenced by peers' and friends' behaviors."

With families growing smaller, the researchers suggest that peer groups are taking the place of siblings. It's natural to want your child to grow up around cousins. Aside from the socialization benefits, there are some cost-sharing benefits as well (free babysitting arrangements, carpools, etc.) as having children around the same time. Whereas in the past, people might have looked to siblings for such support, it may be now that they look more to friends.

"We assume that having friends with whom individuals can share their experiences as parents may reduce the uncertainty associated with parenthood," the authors write.

High school, whether many of us would like to admit it or not, can set the trajectory of the rest of our lives. And a lot of times, it's for the better. For one, consider that lifelong friendships are correlated with longevity. In times when individuals are nomadic, and families are smaller, it's nice to know that the influence of a good friend doesn't fade, even over a decade.