Critical New Testament scholarship generally treats Luke's infancy narrative, including the Annunciation, as a carefully composed theological introduction to his Gospel rather than as a transcript of events witnessed and later reported by participants. Scholars including Raymond Brown, in his standard critical commentary on the infancy narratives, note close parallels between the Annunciation scene and Hebrew Bible annunciation type-scenes, including the announcements of the births of Isaac, Samson and Samuel, a literary pattern Luke appears to be working within deliberately rather than reporting an unprecedented, unpatterned event.
This does not mean scholars uniformly deny any historical kernel behind the narrative, but it does mean the specific details, Gabriel's appearance, the precise wording of the exchange, and the circumstances of Mary's response, are read primarily as Luke's theological composition, written decades after the events they describe and shaped by his aim of presenting Jesus's conception as directly willed and initiated by God from its very beginning.
The doctrine the Annunciation supports, that Jesus was conceived through the operation of the Holy Spirit without a human father, a virginal conception, became a settled point of Christian doctrine affirmed in the major early creeds, even as its historical basis, resting entirely on the infancy narratives of Matthew and Luke and absent from the earlier Gospel of Mark and from Paul's letters, remains a matter that critical scholarship distinguishes clearly from its later doctrinal status.