Paul attests to the virgin birth indirectly, in the following ways:
1. Adam Christology of Romans 5 and 1 Cor 15.
2. Use of Greek terminology of Galatians 4.
Adam Christology of Romans 5 and 1 Cor 15
Romans 5:14-19 (RSV)
14 Yet death reigned from Adam to Moses, even over those whose sins were not like the transgression of Adam, who was a type of the one who was to come. 15 But the free gift is not like the trespass. For if many died through one man's trespass, much more have the grace of God and the free gift in the grace of that one man Jesus Christ abounded for many. 16 And the free gift is not like the effect of that one man's sin. For the judgment following one trespass brought condemnation, but the free gift following many trespasses brings justification. 17 If, because of one man's trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ.18 Then as one man's trespass led to condemnation for all men, so one man's act of righteousness leads to acquittal and life for all men. 19 For as by one man's disobedience many were made sinners, so by one man's obedience many will be made righteous.
1 Corinthians 15:20-22 (RSV)
20 But in fact Christ has been raised from the dead, the first fruits of those who have fallen asleep. 21 For as by a man came death, by a man has come also the resurrection of the dead. 22 For as in Adam all die, so also in Christ shall all be made alive.
1 Corinthians 15:45-50 (RSV)
45 Thus it is written, "The first man Adam became a living being"; the last Adam became a life-giving spirit. 46 But it is not the spiritual which is first but the physical, and then the spiritual. 47 The first man was from the earth, a man of dust; the second man is from heaven. 48 As was the man of dust, so are those who are of the dust; and as is the man of heaven, so are those who are of heaven. 49 Just as we have borne the image of the man of dust, we shall also bear the image of the man of heaven. 50 I tell you this, brethren: flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable.
Use of Greek terminology in Galatians 4
Galatians 4:4-5 (RSV)4 But when the time had fully come, God sent forth his Son, born (ginomai) of woman, born (ginomai) under the law, 5 to redeem those who were under the law, so that we might receive adoption as sons.
Galatians 4:23 (RSV)23 But the son of the slave was born (gennaō) according to the flesh, the son of the free woman through promise.
Galatians 4:28-29 (RSV)28 Now we, brethren, like Isaac, are children of promise. 29 But as at that time he who was born (gennaō) according to the flesh persecuted him who was born according to the Spirit, so it is now.
Also in Gal 4:4, Paul mentions that Jesus was “born of a woman” without specifying a human father. Some theologians suggest that this could be an indirect reference to the virgin birth.