Info taken from pregnancyandbaby.com
What your baby's up to:
This week marks the beginning of what is referred to as the fetal period, which lasts until birth. Your baby's body systems, such as circulatory, nervous, reproductive and digestive, are fully formed during this time. Your baby's heart is beating approximately 160-170 beats per minute. Your baby is growing fast and is now approximately 27 - 35 mm or 1.06 - 1.38 inches with 1/2 of that length being attributed to the head. He weighs between 3 - 4 grams, or less then 1/2 an ounce -- that is about as much as four paper clips.
Also, your baby will become much more active then before, but unfortunately, still too small for you to notice. He will be moving his arms and legs, which can only be seen on an ultrasound. Your baby's joints are fully formed, as are his tiny hands, feet, fingers and toes. Even this young, he would be able to grab an object if it were placed in his hand. Your baby's eyes are openly most of the time but they will not remain that way. The eyelids are beginning to fuse, and they will stay shut until you reach approximately 25 to 27 weeks. The external genitalia is beginning to be able to show your baby's sex, however it will be many weeks before even an ultrasound can tell if you are having a boy or a girl. Both the external ears and upper lip are completely formed now. However, your baby's biggest accomplishment this week is the disappearance of the tail!
Also, your baby is now taking breaths. This breathing activity is noticeable as he "breathes" amniotic fluid. Oh, and he is beginning to urinate as well.