When a doctor tells Pam and Nick, one of the three couples in the tri-partite “Baby!”, that trying to conceive can test a marriage, you really wish he’d sound the alarm to the other two pairs. The warning would only be fair, but it might also stop the development of this fun — if campy — musical comedy, so it’s probably best left unsaid.

“Baby!”, directed by Hayley Ryan ’08, is the story of what happens when you can’t be sure of the love, the marriage or the baby carriage. Set at a nameless college, the plot follows three couples in their occasionally-intersecting struggles with pregnancy. The juniors, requisite semi-edgy, good-boy musician Danny (Sam Tsui ’11, who plays this convention with unusual vitality) and his doting, optimistic girlfriend Lizzie, find that contraception isn’t fool-proof, while the logical dean, Alan McNally (Mike Pacer ’10), and his practical wife Arlene, find that being three-time parents in their 40s isn’t good protection either. Pam (the endearing Hannah Friedman ’08), a youthful women’s basketball coach, and her husband, Nick (Tommy Crawford ’09), wish such accidents were theirs.

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The introductions, as one would imagine, take some time, but, once they’re done, the plot settles into a short lull. Characters just sing about their feelings of expectancy — a lot, and often more than once. Unquestionably those of ’80s musical theater (strong synth), the songs are pleasant, and a few of the tunes are memorable. The pit echoes too much to hear the actors in one or two big moments, but mostly the voices carry happily through on lyrics about passing out, sperm and love. A chorus does sing short ditties to mark the passage of time, which becomes annoying, but the transitions are short, and it’s worth seeing the rather ingenious hiding of set pieces in a theater with no backstage to speak of.

The staging itself is occasionally repetitive, but there’s enough freshness to demonstrate that a small space need not be limiting. Many moments in the Sondheim-inspired storytelling call for unconnected scenes to happen simultaneously on stage. Trying to follow the three couples, each in their own spot-lit circle, can be stressful.

Pam and Nick’s story springs out of the lull the soonest, and their playful interactions remind us how enjoyable the show is when it explores the unexpected results and conflicts that a pregnancy (or a lack thereof) can cause for parents. Their doctor orders a series of scheduled rendezvouses and yogic positions, and their humor through the purgatory is almost touching. Pretty soon, the other two narratives join Pam and Nick’s in speeding up, and all three then proceed in mostly humorous and surprisingly divergent directions.

The cast as a whole has great comedic timing, even when they’re forced to stretch for a few clichéd, “Father of the Bride, Part II”-style domestic situations. Later, when the characters’ humor fails them, the shift to drama is seamless. In one particularly touching scene in the second act, Lizzie and Arlene must confront the unexpected resentment and confusion that the other’s presence brings. They go through honestly, without resorting to melodrama, which is fitting since the lack of the conventional narrative of joyful pregnancy is what’s causing them so much confusion and trouble to begin with.

The scene shows just how much dramatic possibility went untapped because the plots rarely braid together (and their occasional overlap is that much less plausible as a result), but it also reveals that “Baby!” is a misnomer: The baby is an uninteresting eventuality when compared with negotiations over the future of one’s partnership.

Or rather it confirms this: We know it right from the beginning. Even during the early lull, Danny winces at the thought of a daughter, while Lizzie swoons over the idea. Alan starts sputtering in the excitement of rediscovered youth, while Arlene looks like someone asked her what her least favorite meatloaf recipe tastes like. The couples have a few differences to resolve.

These moments are small, funny portents of the problems to come, and they suggest that the foibles aren’t confined to those rare 40 weeks. Coming soon, “Terrible Twos: The Musical?”