“Motherhood” begs the question asked by the mother of this trying comedy: “Why aren’t there any decent comedies about motherhood?” Writer-director Katherine Dieckmann, a former Village Voice contributor, says in her press notes: “My goal as a filmmaker is to explore the full dimensionality of my characters’ lives with as much humor and empathy as possible.” Maybe if she settled for exploring dimension instead of dimensionality, we would empathize more with Eliza Welch (Uma Thurman) and find more humor in her hectic family life. Dieckmann only asks that the leggy, uncombed Thurman deliver two degrees of frazzled and two gradations of flustered as she plans her daughter’s sixth birthday party in their rent-controlled walk-up. Tourists clog the sidewalk gawking at the exterior for “Seinfield” episodes, and a film crew takes up the parking spots in the West Village. As in “Julie & Julia,” a blog is Eliza’s portal to fulfillment. “I want to finish the laundry and a complex sentence,” she posts. “Is that too much to ask?” No, but it’s more than “Motherhood” can answer. With Anthony Edwards, Minnie Driver and Jodie Foster as a mom pestered by paparazzo. 90m. (Bill Stamets)