They summoned the goddess Yogamaya and experienced her transfer the fetus through the womb of Devaki towards the womb of Rohini (Vasudeva's other spouse who lived together with her sister Yashoda across the river Yamuna, inside the village of cowherds at Gokulam). So the child conceived in a single womb https://f004.backblazeb2.com/file/DigitalAsset/SouthernCaliforniaSurrogacy/Becoming-A-Surrogate-In-Southern-California.html