What is the significance of the word, "v'Hinei"?
Rashbam: The Torah often uses this word to introduce a Chidush. 1
Seforno: It turned out just as everyone present thought - that she was expecting twins. And since one would have expected the smooth one (whose birth must have been easier) to be born first, when the first one emerged full of hair, they called him 'Esav,' in that he must have been forced out 2 by his brother (who pushed him out first).
Why is the word 'Te'omim' missing an 'Alef' here, as opposed to later, regarding Tamar (38:27), where it is written in full?
Rashi: To distinguish between Rivkah, one of whose twins was a Rasha; and Tamar, whose twins were both Tzadikim. 1
Ha'amek Davar: This teaches that even in the womb they were not [similar] twins, rather, they were distinct.
Gur Aryeh: What is the derivation? In our verse, the word is spelled Sav-Vav-Mem-Mem; the lack of an Alef indicates that one of the twins would be wicked. Had it been spelled in the normal way, Sav-Alef-Mem-Mem, it would not indicate anything. In verse 38:27, it is written in full, Sav-Alef-Vav-Mem-(Yud-) Mem; the extra Vav means that both would be righteous.
What is the significance of the fact that 'Rivkah's days of pregnancy were completed,' a term that is not used with regard to the pregnancy of Tamar (Yehudah's daughter-in-law) (38:27)?
Rashi: To distinguish between Rivkah's pregnancy, which lasted a full nine months, 1 to that of Tamar's, which lasted only seven.
Malbim: Once the time was completed, the fighting stopped. This hints that once the time for the redemption (which is called Leidah) comes, the opposition of Esav towards Yaakov will cease.
Ha'amek Davar: Once the time was completed, it was a normal pregnancy. This hints that even though the start of the nations of Yisrael and Edom was wondrous, unlike other nations, afterwards they will conduct like all nations.
See also Targum Yonasan.