The development of the entire fetal brain begins in the 5th-6th weeks of pregnancy and will continue until the fetus is delivered. There are several critical periods in the development of the brain as follows: 1. Brain formation period: The early stage of pregnancy, usually between the 2nd and 14th weeks of pregnancy, is a critical period in the development of the fetal nervous system, when the fetal spinal cord gradually grows all over the spinal canal. The initial primary neural tissue is formed around the 18th day after fertilization of the egg, and around the 5th week, cells begin to divide in large numbers, at which time the cerebral hemispheres are formed and the cerebral cortex begins to develop gradually. In the seventh week of gestation, two brain vesicles may appear in the forebrain, while some nerve cells begin to form dendritic cells and axonal cells. 2, brain cell proliferation period: the development of the fetal brainstem, nerve roots and brain tissue usually begins in the middle of pregnancy, and the brain subdivisions may appear in the 15th week of gestation, which can generally be divided into forebrain, midbrain and hindbrain, and gradually begin to differentiate into the emergence of neural tissue fibers cell membranes, and nuclei. and nuclei. From 20 weeks of gestation the fetal brain sulcus and brain gyrus begin to develop, and at about 24 weeks of gestation the sulcus will appear on the surface of the fetal brain.3. Active brain growth period: At 30 weeks, the fetal brain development is basically complete, but at this time the neuronal development affecting the brain neurodevelopment continues dendritic synapses until after birth, laying the foundation for many future abilities of the fetus, such as visual, auditory, olfactory, gustatory, vestibular, kinesthetic and other development. Therefore, it is recommended that pregnant women should take folic acid supplements in the early stages to avoid causing damage to the fetal nervous system and to increase the amount of foods that are beneficial to fetal brain development, such as fish and shrimp, walnuts and egg yolk, which help promote fetal brain development.