From the Shorter Catechism

Q. 22. How did Christ, being the Son of God, become man?

A. Christ, the Son of God, became man, by taking to himself a true body and a reasonable soul, being conceived by the power of the Holy Ghost, in the womb of the Virgin Mary, and born of her, yet without sin. Heb. 2:14, 16; Heb. 10:5; Matt. 26:38; Luke 1:27, 31, 35, 42; Gal. 4:4; Heb. 4:15; Heb. 7:26.