During pregnancy, there are various reasons why a shadow may be visible in the baby's tummy on an ultrasound scan. One possibility is that it could be an artifact caused by the position of the baby or the angle of the ultrasound probe. Another possibility is that it could be an indication of excess gas or fluid in the baby's stomach. In some cases, a shadow may also indicate an abnormality or growth within the baby's abdomen. To determine the exact cause and significance of this shadow, further evaluation such as additional imaging or tests may be necessary. It is important to discuss your concerns with your healthcare provider who can provide more specific information based on your individual situation.