ABSTRACT
Development of the central nervous system (CNS) begins as early as the 2nd postconceptional week, proceeds throughout gestation, and continues long after birth. Although some histogenetic processes are not finished until puberty, motor development and motor behavior events are very active in early pregnancy. 1–4 During the 1st trimester of gestation, the most intensive histogenetic process is neurogenesis. Neuronal migration and synaptogenesis begin almost simultaneously with proliferation, although their intensity increases during the 2nd trimester. The intensity of developmental processes, as well as their complexity, designates this period as the period of high vulnerability for the developing brain. Harmful events occurring during the 1st trimester of pregnancy can result in a variety of abnormalities of the CNS, from life-threatening morphologic anomalies of neural tube formation to a reduction in the number of neurons and consequently reduced developmental potential. 3
