RiRi just posted a brand new photo of her growing baby bump ... and it looks like she's clearly far along in her pregnancy.

As we reported ... Rihanna is pregnant with her first child, and the baby's father is boyfriend A$AP Rocky. The pregnancy was just revealed Monday, and Rihanna captioned Wednesday's baby bump photo, "how the gang pulled up to black history month."

She also included a bunch of other baby bump pics ... but we've already shown you those. This new photo is much more intimate, she's lifting up a jersey to show what's underneath.

The baby's sex is still unclear ... but Rihanna's dad Ronald Fenty says he's hoping it's a baby girl ... in part because he's already got a couple grandsons.

Tons of celebs are leaving a bunch of cute and supportive comments on Rihanna's post ... so she's not the only one thrilled about the baby bump.