To some the virgin birth seems to be an anti-natural way to be born. To be sure, it is unnatural, but it is not thereby against nature. After all, the virgin conception resulted in a normal nine-month pregnancy and a natural birth…. Something about the event had to be highly unusual. Otherwise it would not qualify as a miracle. And having no male fertilization is highly unusual. This does not make the virgin birth of Christ anti-natural, however, for two reasons.
First, as already noted, even the virgin conception resulted in a normal nine-month pregnancy and a natural childbirth. Furthermore, “if we believe that God created Nature that momentum [i.e., creation of life] comes from Him. The human father is merely an instrument, a carrier… simply the last in a long line of carriers—a line that stretches back far beyond his ancestors … back to the creation of matter itself. That line is in God’s hand. It is the instrument by which He normally creates a man.”
In short, ultimately God’s creative powers are necessary in every birth, to say nothing of one by a virgin. The main difference, then, is not that one is natural and the other is of God. It is that one is a direct and the other an indirect use of God’s creative power.
— Norman Geisler, from Miracles and the Modern Mind, p. 106