It is dogma that Jesus Christ was born of a virgin, who remained as such before, during and after the Birth of Christ. To those who think differently or outright reject this sacred truth, do you not think that God is all powerful and can do as he wishes? If He can create the world from nothing, do you not think that he can allow a child to born from a virgin in the most miraculous manner?
Here is a beautiful meditation from Pope St. Leo I:
“Therefore, when the time came, dearly beloved, which had been fore-ordained for men’s redemption, there enters these lower parts of the world, the Son of God, descending from His heavenly throne and yet not quitting His Father’s glory, begotten in a new order, by a new nativity. In a new order, because being invisible in His own nature He became visible in ours, and He whom nothing could contain, was content to be contained: abiding before all time He began to be in time: the Lord of all things, He obscured His immeasurable majesty and took on Him the form of a servant: being God, that cannot suffer, He did not disdain to be man that can, and immortal as He is, to subject Himself to the laws of death. And by a new nativity He was begotten, conceived by a Virgin, born of a Virgin, without paternal desire, without injury to the mother’s chastity: because such a birth as knew no taint of human flesh, became One who was to be the Savior of men, while it possessed in itself the nature of human substance. For when God was born in the flesh, God Himself was the Father, as the archangel witnessed to the Blessed Virgin Mary: ‘because the Holy Spirit shall come upon thee, and the power of the most High shall overshadow thee: and therefore, that which shall be born of thee shall be called holy, the Son of God.’ The origin is different but the nature like: not by [relations] with man but by the power of God was it brought about: for a Virgin conceived, a Virgin bore, and a Virgin she remained. Consider here not the condition of her that bore but the will of Him that was born; for He was born Man as He willed and was able. If you inquire into the truth of His nature, you must acknowledge the matter to be human: if you search for the mode of His birth, you must confess the power to be of God.” ~Pope St. Leo the Great