During the sixth week of pregnancy, changes to the body are noticeable to the mother. Clothing becomes tighter, and morning sickness has begun. The mother has probably gained a few pounds already, depending on whether she's vomiting from morning sickness or not, according to WebMD.
During the sixth week of pregnancy, the baby is still tiny, only about the size of a BB pellet. It is shaped like a tadpole, and the limbs and eyes are beginning to form. An ultrasound possibly detects the baby's heartbeat by this time. This is a delicate time for baby as it is vulnerable to anything that affects growth, according to WebMD.