The end of the first trimester marks the complete development of the vital organs of the unborn. Also, during this stage, blood formation begins, the brain and nervous system develop, and the foetus also starts to move. In the 2nd trimester, the skeleton hardens, the genitals can be distinguished, and facial expressions of the baby become visible. Besides, hearing, sleeping, and waking phases also develop in the baby during this course. At the end of the second trimester, the unborn start to open their eyes.