https://www.mother.ly/news/its-science-pregnancy-can-be-contagious-among-friends
If it baby announcements seem to come all at once from a close group of friends, research shows there may be a reason: Pregnancy can be contagious.
“A friend’s childbearing positively influences an individual’s risk of becoming a parent,” concluded the authors of a 2014 study published in the journal American Sociological Association.
For the study, the researchers analyzed data on 1,720 women who participated in the National Longitudinal Study of Adolescent Health (ADD Health) in the United States from the mid-1990s to mid-2000s. Tracking female participants who were at least 15 years old in 1995 with home interviews throughout the next decade, the researchers saw that roughly half of the women had a child by the time the final interviews were conducted in 2008 or 2009.
(Click link at top to read the studies)