Your baby is about the size of a blueberry — roughly 8 to 11 millimeters from crown to rump. It is growing fast: about 1 millimeter per day this week.
The brain is the most active construction site. It is dividing into three main sections — the forebrain (which will handle thinking and memory), the midbrain (which will coordinate visual and auditory processing), and the hindbrain (which will control breathing, heart rate, and movement). New neurons are being generated at a breathtaking rate, and the first neural pathways are being established.
Facial features are becoming more recognizable. Small indentations are forming where the nostrils will be. The mouth opening is more defined. Tiny dark circles mark the developing eyes, and the lenses of the eyes are beginning to form. Small bumps on the sides of the head will become the outer ears.
The arm buds have elongated and are beginning to flatten at the tips — these paddle-like ends will become hands. The leg buds are slightly behind the arms in development but are growing rapidly. Internally, the liver is producing blood cells (a job it will handle until the bone marrow takes over later in pregnancy), and the kidneys are in their early stages of formation.
For a look at what happened last week, see our week 6 guide.