Socialist states aspired to create modern, egalitarian societies with healthy citizens. Over the four decades of state socialism, experts debated whether premature children could achieve normal long-term mental development and full societal integration. This article analyses expertise networks to comparatively explore medical discussions regarding premature infants’ long-term development in Hungary, Poland, East Germany and Czechoslovakia. We examine how medical expertise interacted with psychology and sociology, analysing the shifting impact of these disciplines across time and space and how state–expertise relationships differed among disciplines. Two significant turning points emerge. First, in the late 1950s and early 1960s, psychology’s resurgence facilitated the identification of mental delays in preterm children, sparking systematic expert interest in their development. Second, beginning in the early 1970s, experts inspired by transnational knowledge exchange emphasized socio-environmental factors’ influence. While East-Central European experts referenced their Western counterparts, they diverged in framing gender and class dynamics. Socialist experts adopted a less gendered approach to parental roles, contrasting with Western studies emphasizing maternal care and paternal occupation. Although less classist than Western perspectives, 1970s medical expertise incorporated class indicators to analyse premature children’s socio-environments, aligning with country-specific sociological approaches. These developments indicate broader societal shifts within socialist societies.