What did research before 2015 indicate about the environment of babies in the womb?

Research prior to 2015 suggested that babies in the womb existed in a sterile environment. This view was based on the belief that the uterus and amniotic fluid were free from microbiota, meaning that there was no microbial life such as bacteria present during fetal development. This concept led to the understanding that significant microbial exposure begins largely at the time of birth, which has implications for how the infant's immune system develops and interacts with the environment after delivery.

The sterile womb hypothesis was also foundational in understanding how early life experiences, particularly those related to microbiota exposure, could impact health outcomes. The belief in sterility was later challenged by emerging research that suggested the possibility of a microbiome even before birth, altering the understanding of prenatal environments. Nonetheless, the established view before 2015 emphasized a largely sterile womb prior to the introduction of microorganisms at birth.