According to the trusty Internet Movie Database (
www.imdb.com), Gabrielle Carteris was born in 1961, and joined the cast of 90210 in 1990, which would have made her 29. 29 plus 13...42? Yikes
Maybe her pregnancy was a way for the writers to slowly write her off the show, being that she was that much older. With a baby, she really didn't have time for the West Beverly/California University shenanigans.