5 weeks fetal development
By the beginning of week five, the cluster of cells is just recognizable as an embryo and is visible as a tiny nubbin of tissue on the ultrasound scan. Although little bigger than a nailhead, all the building blocks for your baby's vital organs are already in place.
The primitive heart begins to form and starts to circulate blood. At 5 weeks of fetal development, it is simple tubelike structure.
A digestive system is in place, although it will be many months before it is capable of functioning. A tube now extends from the mouth to the tail of the embryo and from this tube the stomach, liver, pancreas, and bowels will develop.