In "Juno," the new, life-affirming teen-pregnancy comedy, our spunky 16-year-old heroine is aghast to learn she's been knocked up. "I was thinking I'd just nip it in the bud," Juno tells her best friend. "They were talking in health class about how pregnancy can lead to an infant."

This is "Juno's" tone, especially when the charismatic Ellen Page is onscreen handing out the bons mots: irreverent, witty and verbally adroit. It's the kind of movie that should arouse choruses of "This is no laughing matter!" from self-appointed moral guardians everywhere.

Just one problem with that: She doesn't nip it in the bud, even after calling a clinic to "arrange a hasty abortion." She makes like Madonna in "Papa Don't Preach" and keeps her baby (or puts it up for adoption, anyway). In the process, she solidifies the year's least likely comedy trend. For all of the rhetorical hand grenades lobbed at Hollywood's moral vacuum, 2007 will go down as the year of the pregnancy comedy.

And there's not an abortion in sight.

Not in "Knocked Up," the Judd Apatow hit that matches Seth Rogen's underachieving slob Ben with Katherine Heigl's go-getter babe Alison as nervous parents-to-be.

Or "Waitress," the story of a pie-obsessed Southerner, Jenna (Keri Russell), married to an insecure lout. She ends up having an affair with her ob-gyn but first she tells him the score: "I'm keeping it but I'm just telling you I'm not so happy about it like some other people might be."

The baby-keeper cause-film of the year has been "Bella," an earnest indie about a pregnant waitress (yes, another one) befriended by a soccer star. "Bella" has been endorsed by everyone from Texas Gov. Rick Perry, who wrote a "review" of the film, to Laura Bush. Here's guessing the same people won't be singing the praises of "Juno."

The pregnancy comedies aren't particularly interested in politics, but they form a fascinating case study for observers of the culture wars. In one sense they're pro-life; some of the characters in "Knocked Up" (not the expectant ones) subsist on a diet of bong hits but can't even bring themselves to utter the word "abortion." (They end up going with "shmshmortion.")

Juno makes it to the clinic early in the film but flees when a protester tells her that her fetus already has fingernails.

But Juno, Jenna and Alison have more in common than an aversion to shmshmortion. They're all strong-willed women who have the wherewithal to make a choice. They choose to see their pregnancies through, but they do so on their terms - even Jenna, who can't fathom the idea of raising a child with her husband.

She composes a letter to her unborn baby about her mixed feelings on bringing another life into her world: "Many of the people I've met are not worth meeting. Many of the things that happen are not worth living through." She may hate her husband, but she loves her baby, and the birth somehow liberates her enough to cut the hubby loose. Here motherhood isn't just sanctified; it's also emboldening.

Jenna's missive to her baby lays down another common denominator of the pregnancy comedies: These mothers are determined to have their babies, but they're also gravely concerned about the conditions, global and familial, that their kids will enter.

Juno is a font of risqué humor. When her child's prospective adoptive parents (Jennifer Garner and Jason Bateman) explain that they've had a hard time finding a baby, she offers up this gem: "You should have gone to China. I hear they give away babies like free iPods. They pretty much put them in those T-shirt guns and shoot them out at sporting events."

But her wishes for her baby are about as basic and humane as possible: "I just want the baby to be with people who are going to love it and be good parents," she explains in a rare moment of minimal hilarity.

Like her fellow comedic moms-to-be, Juno is deceptively responsible and serious-minded about what faces her. In "Knocked Up," Alison reads every baby book available and is incensed when Ben doesn't. Jenna visits her ob-gyn religiously (even before she starts sleeping with him).

Two of these babies (the two that aren't birthed by a teenager) are conceived in a drunken state, but when the chips are down the ladies are all business, comedy or no.

None of the pregnancy comedies can be reduced to an issue, which is one reason why they're good movies. But if you're the type who looks for a life lesson, then try this one: Family values come in infinite shapes and guises.

A single mom who loves her child enough to divorce her worthless husband? That's a family. A slob and a babe who learn to love each other after she gets "Knocked Up"? That's a family. So is an adoptive mother who wants a child so bad it hurts, a pain readily recognized by the sassy teen who decides not to nip it in the bud. *