The belief that women rapidly lose their fertility as they age has been popularized using biological findings about “aging” of eggs (or oocytes) in the ovaries. Recently, Japan has experienced national propaganda based on such a belief. In the past decade, doctors and medical organizations have broadcasted information about age-related fertility decline for women in their 20s and 30s. Their theory has spread on mass media without any scrutiny, creating a social pressure on women to bear children as early as possible. Such information has also served as evidence for the government's pronatalist policy of getting young people married.

This paper traces the history of the belief and explores how it emerged, progressed, and spread as authorized “scientific” knowledge by focusing on the graphs frequently used to support the “egg aging” discourse.

A literature survey revealed the following facts that exemplify the role of traditional experts and journalists in creating the “post-fact” phenomena. The graphs, seemingly quoted from the scientific literature, were actually fabricated, falsified, trimmed, or misinterpreted. Doctors manipulated graphs, supported it with unreachable citations, and provided insufficient or distorted explanations about the data and methods. These techniques are being used in the field of obstetrics and gynecology since the 1980s. Journalists have recently contributed to the propaganda, using sensational language to polish the message. During the development and radicalization of the discourse, no social mechanism was performing the fact-checking function. The “egg aging” propaganda, endorsed by medical authorities, aroused people's feeling about the alarming prospect of the country's low birthrate and shrinking population. It eventually achieved hegemony in public debates in 2010s Japan.