Loom

Looms were devices used by Time Lords to perpetuate their race in the wake of the Pythia's Curse. Unable to procreate sexually, the Time Lords had to rely on the Rassilon-invented devices to "weave" new life from genetic material. (PROSE: Cat's Cradle: Time's Crucible, Lungbarrow)

However, there were instances of womb-born children during the period where Looms were in use. Rassilon passed a decree that "only the Loom-born shall inherit the Legacy of Rassilon", and enforced this decree by wiping out the womb-born. (PROSE: Cold Fusion) There were later instances of womb-born Gallifreyans living amongst the Loom-born. (PROSE: The Infinity Doctors)

According to Leela, each Family on Gallifrey had their own "Family Loom" which they used to create new members of their Family. She felt pity for Gallifreyans, because the Looms prevented "true children" from existing on their planet. Gallifreyans were born as "full-grown adults" (that's what Leela thought, which was later stated wrong), although they were child-like at the time of their birth, and had to mature mentally like any young life-form. The genetic relationship between people originating from each Family Loom was lateral rather than direct, meaning that people from the same Loom were "cousins" of each other. (PROSE: Lungbarrow)

Looms also kept a tally of all the people they birthed, and could normally indicate how old each of its "offspring" was and how many regenerations each had gone through. Data from all the Family Looms on Gallifrey was sent to the Bureau of Loomographic Records, which served as a central repository of genetic information.

A Loom was given to 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, for example, was allotted forty-five cousins. When a member of a Family died for the final time, the Loom would weave a new cousin into the Family. Cases did exist when an additional cousin was woven, such as the Doctor's cousin Owis, but were extremely rare, as this was illegal. (PROSE: Lungbarrow)

When he was only five years old, the Doctor boasted that he could remember existing in the Loom before he was actually 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...""

- The Doctor

The Eighth Doctor once said that he was loomed, yet remembered having parents and a childhood. He knew that one of these was a dream, but could not recall which. (PROSE: The Shadows of Avalon)

Looms were used to mass-produce soldiers during the War. (PROSE: The Taking of Planet 5)

When Rassilon and the Cyberman conquered Gallifrey, they used Looms to trap captured Time Lords in a state of perpetual regeneration, where the Looms could harvest the energy created. The Cybermen later linked it to the Cyberiad and the Eye of Harmony, where they planned to alter history. The Twelfth Doctor and Rassilon countered this plan by using the energy to regenerate the universe and return history to normal. (COMIC: Supremacy of the Cybermen)

Behind the scenes

 * Like many ideas and concepts in Doctor Who, this has not been referenced on-screen, and can be seen to contradict other sources. There have been many statements by the Doctor and others referring to him being a "boy" or showing the Doctor and other Time Lords as children.
 * In his production notes in DWM 482, Steven Moffat, while obliquely referring to this discrepency, claimed that it was "reasonable to assume that Time Lords [met] and marr[ied] and mate[d] in much the same way" humans did. He acknowledged "some highly inventive material in the Virgin New Adventures books contradicting this" and described the New Adventures as "a separate (and equally valid) continuity" to the modern BBC Wales TV series.