This is an example of how the witches toyed with Macbeth. When they first met with him and Banquo, they told Macbeth two truths and offered one prediction (Act 1, scene 3):
"...All hail, Macbeth! hail to thee, Thane of Glamis! All hail, Macbeth! hail to thee, Thane of Cawdor! All hail, Macbeth, that shalt be King hereafter!"
Then, in Act 4, scene 1, the witches show him equivocating apparitions who, as Macbeth later says "lie like the truth." The second apparition is a bloody child who says,
Be bloody, bold, and resolute; laugh to scorn
The power of man, for none of woman born
Shall harm Macbeth.
The bloody child is Macduff, who, as a Caesarian section by birth was, as Macduff himself says, "from his mother's womb Untimely ripp'd." That's why the child was bloody, for it had on it the blood of the Caesarian procedure. Of course this confounds Macbeth because the witches, through the apparition, were merely playing with words. A child who is born by Caesarian section is still "born of woman" but not in the strictest sense of a normal, birth-canal birth. (Why he was a Caesarian is not important, nor is the condition of Macduff's mother at the time of or after his birth). Very tricky indeed, especially so for literal-minded Macbeth.
In Shakespeare's Macbeth the Witches' prophecy was that "...none of woman born/ Shall harm Macbeth" (IV.i). Unfortunately for Macbeth, the Scottish nobleman Macduff was "from his mother's womb/ Untimely ripped," in other words born by Caesarian section, a procedure which would mean he was not born naturally "of woman" (V.vii). Macduff was the only agent capable of destroying Macbeth.