Your baby's eyelids and eyebrows are well developed by this week of pregnancy, but the eyelids remain fused. The cells that are destined to become your baby's fingernails were present at 10 weeks, and the cells for the toenails were present four weeks later.
Now, at 23 weeks, the nails are just beginning to make an appearance at the base of the nail bed. The nails will grow continuously throughout life, but it will be several weeks before they have reached the tips of the fingers and then the toes.
Your baby's skin is developing quickly and often appears wrinkled at this stage; it is as if the baby has yet to grow into it. Your baby is now covered in extremely fine and short hairs, known as "lanugo." This layer of hair will be almost completely lost before birth. The hairs help trap vernix onto the surface of the skin; this is the white, greasy layer that you often see in patches on a baby's skin at birth. It collects in the skin folds and creases and helps protect the baby's skin not only from the water content of the amniotic fluid, but also the waste products within it.
As your pregnancy advances, your baby's kidney function is improving and the amniotic fluid produced becomes increasingly similar to urine in its composition.