Loom

The Loom (or Looms) were a genetic weaving construction created by Rassilon following the Pythia's curse of sterility on Gallifrey. (NA: Cat's Cradle: Time's Crucible) They could literally weave a fully grown (though not matured) Gallifreyan.

A loom was set into each of the Houses of Gallifrey and each House had a specified number of Cousins which could exist in the Family at any given time. The House of Lungbarrow was alloted fourty-five Cousins, and when one of these died for the final time, the loom would weave a new Cousin into the family. Though cases did exist when an additional cousin was weaved (such as the Doctor's cousin Owis). (NA: Lungbarrow)

One very young Time Lord in the House of Lungbarrow once claimed that he could remember existing in the loom before he was born:

“I can remember waiting to be born…It was like being all strung out. All unravelled inside the Loom. I was spread really thin…I couldn’t think. Not put thoughts together. … But I knew where I was and what was happening. I couldn't wait to get out. And then I was born. My lungs nearly burst. The first rush of air was so cold....”

(NA: Lungbarrow) Whether or not this claim is true is uncertain, as it's possible the boy in question was simply trying to provoke his tutor at the time.