Pythia's Curse

Pythia's Curse of sterility was imposed on the Gallifreyans by the 508th Pythia during her suicide. Driven to desperation by Rassilon and the Neo-Technologists' denouncement of magic, as well as her personal inability to find her successor, the 508th Pythia cursed Gallifrey to "wither" and threw herself into the Crevasse of Memories That Will Be.

According to Quartinian, the curse's effect was immediate: fetuses died in their mothers' wombs, including Rassilon's own daughter; and no new children were born on Gallifrey. Faced with extinction in the aftermath of the Great Schism, the Gallifreyans united behind Rassilon and adopted innovations such as genetic Looms, regeneration, and time travel, which enabled them to survive despite the restrictions of the curse. However, the Seventh Doctor disputed this account as a whitewash. (PROSE: Cat's Cradle: Time's Crucible)

According to another account, pregnancy was still possible on Gallifrey, but they were forcibly terminated in accord with a Presidential decree that only the Loom-born could inherit the Legacy of Rassilon. Guards were sent to kill Susan Foreman, who was born one day after the decree and hidden away from Gallifrey. (PROSE: Cold Fusion) Her mother told her that she was the last child born on Gallifrey, just as the Pythia cursed the world. (PROSE: Lungbarrow) By another account, Susan was born one day after a Presidential decree that only the Loom-born could inherit the Legacy of Rassilon, and guards were sent to terminate the pregnancy. (PROSE: Cold Fusion)

The curse was lifted when Leela, a companion of the Doctor who lived on Gallifrey, became pregnant with the child of her Time Lord husband Andred. This ushered in a new era of reconciliation between the (PROSE: Lungbarrow)

According to The Book of the War, the sterility of the Great Houses was actually a side effect of the anchoring of the thread. (PROSE: The Book of the War)

Patience was a young woman at the time of the Curse. (PROSE: The Infinity Doctors)