Host:

Let's visit the growing baby and see what's going on inside of your body.

Listen, that's your baby's heart. Just four weeks after conception, before you may even know you're pregnant, your baby's heart has already begun to beat.

At this point, it's too early to tell who your baby looks like, but you may be surprised at how quickly he or she is developing. The spinal cord is already forming, and the heart has begun its life's work. At the end of the first trimester, just three months along, your baby has arms and legs, and his fingers and toes are well underway. Eyelids, ears, ankles and wrists are already there. All major organs and systems are forming, and will mature over the rest of your pregnancy. At this point your baby is only 2 1/2 to 3 inches long and weighs about half an ounce. Pretty amazing that one so small can be causing so many changes in your body and your life.