🧠 A fetus’s brain development is one of the most extraordinary processes of pregnancy, beginning just weeks after conception. By around week 3–4, the neural tube forms, which will later become the brain and spinal cord. As pregnancy progresses, brain cells (neurons) multiply at an incredible rate, migrating to specific regions and organizing into structures that control movement, sensation, emotions, and thinking. By the second trimester, the brain starts forming distinct areas, and billions of