Your baby is almost 3.5 inches long.
He can now frown, grimace, and pee. His facial muscles are developing; his tiny features form one expression after another due to brain impulses. His kidneys produce urine; he releases it into the amniotic fluid. This will be kept up until birth. His fingers/arms are developing; he can grasp and can suck his thumb. His body is growing faster than his head; his head now sits upon a distinct neck. His arms are growing to a length in proportion to his body. His thyroid starts functioning this week. His genitals develop. For boys, his prostate gland develops. For girls, her ovaries move down her abdomen into her pelvis.
He is developing an ultrafine covering of hair, called lanugo, all over his body. The purpose of this hair is largely for warmth. As fat accumulates on your baby, it will take over the role of keeping the baby warm, and he will lose his lanugo towards the end of your pregnancy. His liver starts making bile this week, and his spleen starts to produce red blood cells. He is also starting to move around a lot. His intestines start to produce meconium; it is the waste that will constitute his first bowel movement after birth.