Eileithyia

Eileithyia is the Greek goddess of childbirth and midwifery, daughter of Zeus and Hera.

The Dungeon Master's Theogony
Eileithyia was born as the third child of Zeus and Hera, sister to Ares and Hebe, and she became the goddess of childbirth.

After Leto became pregnant with Eileithyia's half-siblings, the twins Artemis and Apollo, her mother Hera kidnapped Eileithyia to prevent the Titaness from giving birth until the rest of the goddesses rescued her. After Artemis midwifed the birth of her own brother Apollo, she came to share the same province of childbirth and midwifery with Eileithyia.

Alcmene and Heracles
After Zeus lay with Alcmene and she became pregnant with his son Heracles, the king of the gods proclaimed that the next child to be born of the house of his son Perseus, founder-king of Mycenae, would rule the city and the greater region of Argolis, intending for Herakles, born as Perseus' great-grandson, to become king.

Seeking to spite Zeus, Hera had her husband swear on oath to confirm his proclamation, and Eileithyia, having arrived at Alcmene's house in Thebes to help the latter deliver her son, was forced by her mother to delay Herakles' birth. At that same time, Nikippe, wife of Perseus' son Sthenelos, was herself seven months pregnant and Hera arranged for her to give birth first, resulting in her son Eurystheus becoming king while Herakles was effectively robbed of his birthright.