Stella Dantas, MD OB/GYN: In the early second trimester, which is about 13 to 16 weeks, your baby is starting to develop more rapidly. All the vital structures are in place, they're still too small to be evaluated by ultrasound, which is why we do your anatomy scan a little bit later in the second trimester, but if you were to look on ultrasound, you could easily see the baby's heart, you can see the baby's eye sockets, you can see the baby's mouth, you can see all the bony structures of the baby developing.