In countries with a high prevalence of blood-borne pathogen infections, transmission to infants commonly occurs from an infected mother during pregnancy. Maternal diseases caused by bacteria, viruses and parasites may sometimes be transmitted vertically. For many pathogens, several questions remain unanswered about the pathogenesis of vertical transmission, the relative risk associated with each mode of transmission, the rate of transmission from mother to child, and the factors that might contribute to the efficiency of transmission. There is also a need to quantify the contribution made by intrauterine versus intrapartum events. Here, the feasibility of some new emerging blood-borne hepatitis viral pathogens (hepatitis G virus, hepatitis SEN virus and hepatitis TT virus) passing through the placenta was analyzed based on a consideration of nonostructure level. Based on the particle size as a single factor, it is hereby proposed that the transmission of the studied viruses via the placenta is difficult. Possible infection due to other processes, especially intrapartum infection due to micro-trauma delivery, similar to HIV infection, might be a more important route of vertical transmission.