P2X-787
From The Stargate Omnipedia
Planet visited by SG-13, under the command of Colonel Dave Dixon, where the team encountered a form of life that was similar in appearance to an ultrasound picture of Senior Airman Simon Wells' baby -- or so says the team members of SG-13.
KEY EPISODE
Heroes, Part 1 - While looking over the ultrasound image of Wells' unborn child, Boswell references the time they visited P2X-787 and encountered a creature with a similar appearance.