Your little one will be putting on weight this week--as much as 2.5 oz (71 g)--but that's just for starters. The next 5 weeks will be a period of intense weight gain.

That's not the only way in which baby is growing. His cerebrum (the surface of the forebrain and seat of the intellect, motor control, and memory) has started acquiring folds and wrinkles, although compared to an adult brain it still appears quite smooth. This provides greater surface area for cell-to-cell communication. Other regions of the brain--areas that control emotion, hunger, sexual drive, balance, and other basic impulses--are emerging, but remain less developed. About this week, too, your baby begins to have rapid eye movements (REM), the eye motions seen during the stage of sleep where dreaming occurs.