Both scenes are pretty far into the game, just so you know. Lots of other great characters and sex scenes along the way, so you won't be bored.
Tanya - your girlfriend from college, if you don't select the choice to not have safe sex with her when asked, she won't appear in the game at all. If you're not safe, she turns up late in the game pregnant.
Paveena Patel - I won't spoil anything about her beyond that she's a different characters sister, the choices that lead to her getting pregnant are pretty obvious.