This poem begins with a pronouncement. "Perfection," the speaker declares, "is terrible": sterile and "cold as snow breath," it "cannot have children." Personified as a woman, "perfection" here is not an aspirational figure; she's infertile and frigid. What's more, she begins to seem like a cruel goddess, holding other women back from an embrace of "life"—and especially the new lives of "children."
The specific way that perfection does this is through a restriction on "the womb": the uterus, that is. Normally, the speaker suggests, women's wombs are a place of fiery, bloody, sprouting energy—far from that chilly "snow breath." Take a look at the symbols, similes, and metaphors the speaker uses in this surreal picture of the wildness of the life inside women's bodies:
Where the yew trees blow like hydras,
The tree of life and the tree of life
Yew trees are a common symbol of both death and rebirth: evergreen, they're often planted in graveyards. What's more, the yew trees here are "like hydras"—mythical, many-headed monsters. Besides suggesting that the womb is a dangerous place as well as a nurturing one, the image might suggest the literal anatomy of a uterus, with its branching fallopian tubes. And the "tree of life"—an image so important the speaker needs to repeat it—suggests not just the eternal growth of life itself, but connectivity, family, and linked generations—as in "family tree."
Anything that "tamps" (or squashes down and represses) the power of such a "womb" must be terrible indeed! But icy perfection, the speaker says, has that power. Under its thrall, all those wild, lashing, fertile trees are left:
Unloosing their moons, month after month, to no purpose.
Those "moons" are eggs—released every month, then washed away by the menstrual cycle. (And notice how the round assonant /oo/ of "unloosing their moons" evokes both the shape of the full moon and the shape of an egg.) Unfertilized, this speaker feels, those poor moons serve "no purpose."
This speaker, readers can already feel, has strong feelings about women's bodies and women's power. Pregnancy and childbirth, to her, are a rebuke to a kind of sterile "perfection" that has no room for such power. More than that, reproduction seems to strike her as an ultimate "purpose": a woman's connection to the "tree of life" itself. "The Munich Mannequins" will become a rebuke to all the false ideals that this speaker feels keep women from that connection.