Early postnatal life involves rapid physiological and immunological adaptation as the newborn transitions from intrauterine to extrauterine conditions. These processes are reflected in the circulating plasma proteome and affect key blood functions, including homeostasis, hemostasis, and immune defense. During pregnancy, immune tolerance is tightly regulated within the largely sterile intrauterine environment. After birth, the neonatal immune system undergoes rapid maturation to balance antimicrobial defense with colonization by commensal microbes. This early-life immune development, primarily driven by innate immune mechanisms and maternally derived antibodies, has long-term implications for health and disease and exhibits sex-specific characteristics. To characterize early plasma proteome dynamics, we established a well-controlled cohort of 51 healthy term newborns enrolled in Papua New Guinea (PNG) as part of the NIH/NIAID Human Immunology Project Consortium (HIPC). Peripheral blood samples were obtained from all participants within the first 24 hours of life (Day of Life 0).