In Bereshit 16, Hagar is given to Avraham to bear surrogate children for Sarai. After discovering that she is pregnant, Hagar treats her mistress with disrespect, leading Sarai to mistreat her in turn. Hagar flees into the desert where she is met by an angel who tries to convince her to return to Avraham. The angel promises her:
הִנָּךְ הָרָה וְיֹלַדְתְּ בֵּן וְקָרָאת שְׁמוֹ יִשְׁמָעֵאל כִּי שָׁמַע ה' אֶל עָנְיֵךְ.
Behold, you [are / will become] pregnant and will bear a son, and you shall call his name Yishmael, because Hashem has listened to your affliction.
Why does the angel need to tell Hagar, "הִנָּךְ הָרָה" (generally translated as, "Behold, you are pregnant")? Surely, Hagar is well aware that she is expecting a child? In fact, her disrespect for Sarai stemmed from that very fact, leaving the reader to wonder why the angel is stating the obvious. Did something happen in the interim that caused the angel to explicitly mention the pregnancy?