Kicking off what she dubbed 'the Mother's Day episode,' Tina Fey hosted 'Saturday Night Live' this weekend with a dose of her usual self-deprecation.

Making the most of her six-months' pregnant figure, the '30 Rock' star -- and former 'SNL' head writer -- brought out fellow expectant mom Maya Rudolph for a belly-bump greeting, and a song devoted to their soon-to-be-born children.

The soothing lullaby opened with lyrics such as "I cannot wait to know you," then quickly segued into a raunchy ode to procreation: "You are the proof that we've been doin' it....makin' super sexy heat...your mom and daddy been doin' it!" Mid-duet, the two even had a faux sonogram while each fetus, played by Keenan Thompson and Kristen Wiig, sang along in utero.

After the jump, don't miss Fey's 'SNL' sketch about a horrifying birthing class -- a freak show far crazier than the class she took with Amy Poehler in 'Baby Mama.'

But first, watch the 'Bossypants' author as her maternal monologue turns into a loony musical number: