What shame (disgrace) was Rachel referring to?
Rashi #1: The disgrace of potentially falling into the hands of Esav. 1
Rashi #2: As long as she did not have a son, whenever anything went wrong in the house ('Who broke that plate?' 'Who ate the figs?)', the blame would automatically fall on her. But from now on, she could place the blame on Yakov's (sweet little) son.
Rashbam: The shame of being barren.
Seforno: She was referring to the embarrassment that she felt, due to the fact that Hashem had responded favorably to her sister's Tefilos but not to hers.
Bechor Shor: I will not be less than the [other] mothers. 2
Ha'Emek Davar: Anything that does not fulfill its purpose, it is lacking; there is shame in this. This is especially true for a barren woman. If so, intimacy with her is merely for pleasure!