Baby brain development is the process that occurs within the nine months of pregnancy. During this period, a fetus is vulnerable to developmental disorders related to brain. Many things can affect brain development of a baby inside the womb. This includes inadequate diet, trauma or use of certain drugs or medicines. Genetic factors also play a role in infant’s brain development. Here we will briefly discuss stages of fetal brain development according to week of gestation. Fetal Brain DevelopmentConception and fertilization occur during week 1 and 2 of gestation. The fertilized egg also gets implanted into the uterine wall. The embryo actually starts developing in the third week. At this time, the brain, spinal cord, heart and gastrointestinal tract begin to form. During the fourth gestational week formation of optical stalk and brain parts (the middle brain, fore brain and hind brain) begin forming too. Week 5 is marked by development of early structures that will become the eyes, nose and ears. The arms and legs begin forming as well and may be visible on an ultrasound. At 6 weeks gestation, the brain hemispheres start forming and there is a certain degree of brain wave activity. During this week the neural tube connecting the brain with the spinal cord closes. At week 7 the rapid growth of the brain takes place. During following week, the hind brain controlling the vital activities, such as heart beat and breathing rate, continue to develop. By the end of the first trimester, the spinal cord is clearly developed and the liver, spleen and heart are functioning. Second TrimesterAt 14th to 16th gestation week, brain development is supported by nutrition, which the fetus obtains through the placenta. A fine hair protecting the skin known as lunago starts developing. Rapid growth of torso and sharpening of the sense of hearing takes place too. Physical reflexes are also present. In the following four weeks the skeletal system develops and myelin forms a protective sheath to cover the spinal cord. The fetus is able to detect lights and sounds. The fore brain takes shape and right and left hemispheres develop also. At week 21 lunago completely covers the body of the fetus. Movement control is developed and the spinal cord stretches out. At week 22 the fetus is able to distinguish between sounds. Over next few weeks the brain development is rapid and the nervous system is almost completely formed and regulates different body functions. By the time pregnancy reaches the third trimester, the body of the fetus stores fat leading to weight gain. The brain starts processing information it receives and starts controlling body's temperature and breathing rate. Creases and fissures in the brain continue to form. Apart from the lung, the brain keeps developing until the end of pregnancy.