This is one of the weirdest thing i've ever heard. You must also be wondering how this can be possible. But before you think of anything let me clear it for you. This baby was found in Saudi Arabia. Doctors say its say unique case in the world.
What happened was when the mother was pregnant she has 2 foetus inside her but one foetus grew inside another. Due to this the baby was born with another baby in her womb.

The below are some of the images which show you the baby admitted to a hospital and the xray pics show the other baby hich is growing up inside her.