The Virgin Birth (more precisely, the virginal conception) is attested in a number of ways in Matthew and Luke:-

1. The sharp contrast between the long series of verses that use “begot” and the statement that Joseph was “the husband of Mary, of whom Jesus was born” (Mt. 1:16) clearly implies that a man was not involved in the procreation of Jesus.
2. Mt. 1:18 states, “Before they came together she was found to be with child of the Holy Spirit.”
3. Joseph’s desire to divorce her quietly presupposes that he had had no sexual relations with her (Mt. 1:19).
4. The angel said “That which is conceived in her is of the Holy Spirit” (Mt. 1:20).
5. In citing Isa. 7:14, Matthew called Mary a virgin (Mt 1:23).
6. Joseph “knew her not until she had borne a son” (Mt. 1:25).
7. Twice Luke called her a virgin and said that she was betrothed, which, although almost tantamount to marriage, was not marriage in the fullest sense (Lk 1:27).
8. Mary was amazed at the angel’s announcement that she would conceive, since, as she said, “I know not a man” (Lk. 1:34, ASV).
9. Luke said delicately but explicitly that the Holy Spirit, and not Joseph, would be the cause of the conception (Lk 1:35).

G.W. Bromiley, in ISBE (revised ed.), art. ‘Mary’

Possible allusions to the Virgin Birth (or, at least, doubts about the legitimacy of Jesus’ birth) occur in Mt 13:55; Mk 6:3; Lk 4:22; Jn 1:13, 14; 8:18-41; Gal 4:4-5; Heb 7:3.

If it be thought that the amount of biblical testimony is small, then the following, published by the bishops of the Church of Englad in 1985, offers a response:

‘The amount of direct testimony (in the Bible) to the Virginal Conception is not significantly smaller than that for some other important facts in the story of Jesus. Thus, if we bear in mind the dependence of Matthew and Luke on Mark, there are only two independent witnesses in the New Testament to the institution of the Eucharist, namely Mark and Paul. That Matthew and Luke are independent witnesses to the Virginal Conception is strongly suggested by the fact that their Birth and Infancy narratives have nothing else in common except the names of Joseph and Mary, and Bethlehem as the place of Jesus’ birth. This is also an argument for saying that both the later date of Matthew and Luke and the folk-tale character of the two quite different stories are not significant.’ (Source)