Why does it say above "l'Yaakov Ben" (30:5), and here "Ben Sheni l'Yaakov"?
Malbim: The bigger Chidush is taught first. Above, the Chidush was that the son was attributed to Yaakov. Now, this was already known; the Chidush is that she had a second son. Also for Zilpah's son, it says "l'Yaakov Ben," and "Ben Sheni l'Yaakov" (30:10,12). 1
Targum Yonasan says that Bilhah and Zilpah were freed before Yaakov married them. If so, why is Bilhah called "Shifchas Rachel"?
Ha'amek Davar (to 30:3,7): This shows that she was unlike Hagar, who [after she became pregnant] belittled Sarah. Bilhah continued to [respect and] serve her, like her Shifchah (even though she was freed).