To mangle Gertrude Stein, a sitcom is a sitcom is a sitcom, no matter how much you monkey with the formula. We’re told “In the Motherhood” (7 p.m., ABC) is based on a Web site that solicits stories about motherhood from real women. So why does it seem like the least original and most indifferently conceived new series of the year?

“Motherhood” offers overlapping tales of three best friends with vastly different mothering styles.

Rosemary (Megan Mullally) projects a casual, hands-off approach to single-momdom. She cracks wise about exposing herself in New Orleans and letting the television raise her son.

Emily (Jessica St. Clair) and her nurturing husband are far more pro-active and have become so politically correct that their kids think they are being punished.

Cheryl Hines (“Curb Your Enthusiasm”) rounds out the trio as Jane, a newly divorced mother of a newborn she only dimly understands. Good thing for her, she’s got Horatio (Horatio Sanz), the most diligent “manny” since Eldin (Robert Pastorelli) took care of Murphy’s controversial kid on “Murphy Brown.”

In several disjointed stories, Rosemary attempts to unionize the local nannies, Jane tries to take off from her busy job to spend quality time with the baby while giving Horatio the week off, and Emily’s earnest “stay-cation” scheme unravels.

Despite a game cast, there’s not one real laugh to be found here.

We’re hardly surprised that Emily’s sanctimonious, joyless parenting gives way to something more luxurious.

And Jane’s role as the workaholic yuppie confronted with a high chair recycles comic notions that were rather ripe when Diane Keaton used them in “Baby Boom” back in 1987.

Rosemary’s interaction with nannies, most of them overworked, underappreciated and non-English-speaking, quickly careens from the farcical to the contemptuous to the cruel.

It’s interesting to note that “Motherhood” airs (at least for now) in the place of “Ugly Betty,” a series with some heart about characters on the outside looking in.

In contrast, “Motherhood” asks us to care about poorly defined characters from an exclusive zip code, who, like the writers who have created them, couldn’t buy a clue even when their credit was still good.

Tonight’s other highlights

• The NCAA basketball tournament (6 p.m., CBS) comes down to the sweet 16.

• Randy reminisces about romances past on “My Name is Earl” (7 p.m., NBC).

• The results are read on “American Idol” (7 p.m., Fox).

• Bob Greene hosts “What’s Making You Fat?” (7 p.m., Discovery Health).

• Michael continues to chafe under oversight on “The Office” (8 p.m., NBC).

• “Super Botox Me” (8 p.m., BBC America) looks at patients who take cosmetic surgery to extremes.

• Jack wallows in nostalgia as he approaches the half-century mark on “30 Rock” (8:30 p.m., NBC).

• Morris and Brenner find a worthy cause on “ER” (9 p.m., NBC).

• The crew fights bad weather to lay claim to sunken cargo worth up to $100 million on “Treasure Quest” (9 p.m., Discovery).

• Erica mulls an intervention to stop her sister’s wedding on “Being Erica” (9 p.m., Soapnet).