The embryo now settles into your uterus lining. The outer cells reach out like roots to link with your blood supply. The inner cells form two and then three layers. Each of these layers will grow to be different parts of your baby’s body. One layer becomes their brain and nervous system, skin, eyes, and ears. Another layer becomes their lungs, stomach, and gut. The third layer becomes their heart, blood, muscles, and bones.
The fifth week is when you will miss your period. At this time, most women are only just beginning to think they may be pregnant. Your baby’s nervous system is starting to develop. A groove forms in the top layer of cells. The cells fold up and become round to make a hallow tube called the neural tube. This will become your baby’s brain and spinal cord, so the tube has a ‘head end’ and a ‘tail end’. Defects in this tube are the cause of spina bifida. The heart is also forming and your baby already has some blood vessels. A string of these blood vessels connects your baby to you, this will become the umbilical cord.