How did Mary, mother of Jesus, get pregnant?

{And mention, [O Muhammad], in the Book [the story of] Mary, when she withdrew from her family to a place toward the east.* And she took, in seclusion from them, a veil. Then We sent to her Our Spirit, and he represented himself to her as a perfect man * She said, “Indeed, I seek refuge in the Most Merciful from you, if you are Taqiyya * He said, “I am only the messenger of your Lord to give you a pure boy