The First Thousand Days of Life.

The first thousand days of life, composing the 270 days of pregnancy and the first two years (730 days) of life, is at once a critical and vulnerable time for human development. It is a time in which the human person is to a large extent "embodied," becoming the integrated mind-brain-body-spirit that defines every human being. This embodiment is set in motion at fertilization and continues with the unfolding development of the embryo. By six weeks in utero, the brain is forming via ongoing neurogenesis, neuronal migration, synaptogenesis, and myelination. By the age of two the brain will be 80 percent of its adult size. As the brain develops, it connects to other developing body systems including the immune, endocrine, metabolic, gastrointestinal, cardiovascular and musculoskeletal systems. In this process of interconnection, a human being is shaped by both internal and external environments, both at the stage of the fetus and the stage of the infant. Human well-being and flourishing depends upon making these first thousand days as safe, secure, and healthy as possible. Physician practices, local health policy, and global health advocacy should focus on optimizing the first thousand days. This should include pre-conception care, pregnancy, safe birth, infant nutrition and fostering secure emotional and relational attachments.