Hesiod's Theogony makes Eileithyia a daughter of Zeus and Hera, and Greek myth uses her power over childbirth both to help and, notably, to obstruct: in the story of Heracles's birth, Hera has Eileithyia delay Alcmene's labour specifically so that a rival cousin, Eurystheus, is born first and so receives the kingship Zeus had sworn to grant his own newborn son, a trick that shapes the rest of Heracles's mythology through the labours Eurystheus later imposes on him.
Homer's Iliad refers to Eileithyiai in the plural, goddesses of birth pangs rather than a single figure, suggesting the role could be distributed across multiple divine agents in some strands of tradition even as cult practice at particular sanctuaries addressed a single named Eileithyia. Votive offerings recovered from her shrines are overwhelmingly dedicated by women, consistent with a cult whose petitioners were, unsurprisingly, drawn from those directly facing childbirth, and in some regions her functions were later absorbed into the wider portfolio of Artemis, who came to be invoked for the same concern in areas where a distinct Eileithyia cult had faded. The trick Hera plays at Heracles's birth is told with Eileithyia physically seated with her legs and fingers crossed outside Alcmene's room, a posture ancient sources describe as magically binding the labour shut until a servant tricks her into uncrossing them by announcing a false birth, a detail that treats childbirth magic as something even a goddess herself could be caught by.