A study has found that women are more likely to have a baby after they discover friends from high school have become mothers. Study co-author Nicoletta Balbo, a postdoctoral fellow at Bocconi University, Italy, says that dubbed childhood contagion is a real trend among female high school friends during early adulthood.

The contagion is particularly strong within a short window of time: it increases immediately after a high school friend gives birth, reaches a peak about two years later, and then decreases, becoming negligible in the long-run,' she said.

The study tracked more than 1,700 American women from when they were at least 15-years-old through approximately age 30.

Overall, this research demonstrates that fertility decisions are not only influenced by individual characteristics and preferences, but also by the social network in which individuals are embedded.

'It also shows that high school friends impact our lives well after graduation. Being surrounded by friends who are new parents makes people feel pressure to have kids as well,' said Ms Balbo.

The study, which appears in the American Sociological Review, relies on data from the National Longitudinal Study of Adolescent Health in the U.S.