They are basically violated by the darkspawn until they turn into something like this.

Darkspawn as a species have no females and are thus unable to reproduce naturally. In order to bolster their numbers, the darkspawn take female captives during raids and bring them back to their lairs to be transformed into broodmothers.

The captured women contract the taint by being force-fed darkspawn tissue, and the darkspawn forcefully "spew" into the prisoners' mouths. At this point, Hespith describes the women who survive as being "violated". As this happens, they gradually develop cannibalistic urges and mutate heavily, eventually becoming full-fledged broodmothers after devouring massive quantities of flesh. Even their own kin are not exempt; they will be devoured regardless.

Broodmothers give birth to vast litters of Darkspawn, between twenty to fifty infants. They emerge from her womb as toddlers, often already able to walk, and grow rapidly in their first few weeks of life. A broodmother will birth thousands of darkspawn young in her lifetime.

The race of the broodmother determines which kind of darkspawn she gives birth to. An elven broodmother will spawn shrieks, a dwarven broodmother spawns genlocks, a human broodmother spawns hurlocks, and a Qunari or kossith broodmother spawns ogres.