A comedy about pregnancy seems doomed to a particularly sticky circle of humor hell: How many jokes about maternity underwear and morning sickness can one endure? My original guess would have been about 1.3, but it turns out that Notes From the Underbelly, exec-produced by Barry Sonnenfeld, is no mere ''pregnancy comedy.'' Underbelly stars Jennifer Westfeldt (Kissing Jessica Stein) as Lauren, a sensible thirtysomething who ambivalently decides to have a baby with her doofy, earnest husband(Peter Cambor). On their nine-month journey, they collide with all sorts of odd people, from the Stepford Wife whose business card reads ''Scrapbooker/Mommy'' to the new parents who corner them like undead ghouls so they can reveal how horrific parenting really is. As Lauren's cynical single best friend, Rachael Harris (Fat Actress) provides a needed blast of acid. ''Rainbows,'' she snaps when a pregnant friend asks her to say something nice. Unfortunately, for every scene with Harris, there's a grating counterbalance: Lauren's other friend, baby-voiced Julie (Melanie Paxson from the Glad trash-bag commercials), a chipper, pregnant housewife who's about as appealing as a butter mint stuck in the back of the throat one of those irritating characters who exist only so we can roll our eyes and groan knowingly. Overall, however, Underbelly eschews cliché and makes pregnancy surprisingly laughable including a very funny gag with a breast pump. A phrase I never thought I'd say.