I imagine I read this in high school — it was probably printed in some book we used in a long-forgotten English class. The class itself might be forgotten, but the emotion I felt from the words of the poem are not.
I never remember the name of the poem, but a search on Google (poem about man finding pregnant deer) always finds it for me: Traveling Through the Dark by William E. Stafford.
Traveling through the dark I found a deer
dead on the edge of the Wilson River road.
It is usually best to roll them into the canyon:
that road is narrow; to swerve might make more dead.
By glow of the tail-light I stumbled back of the car
and stood by the heap, a doe, a recent killing;
she had stiffened already, almost cold.
I dragged her off; she was large in the belly.
My fingers touching her side brought me the reason—
her side was warm; her fawn lay there waiting,
alive, still, never to be born.
Beside that mountain road I hesitated.
The car aimed ahead its lowered parking lights;
under the hood purred the steady engine.
I stood in the glare of the warm exhaust turning red;
around our group I could hear the wilderness listen.
I thought hard for us all—my only swerving—,
then pushed her over the edge into the river.
I found the video below this morning. In it the poet talks about the inspiration behind the poem, and reads it at the end.
When I first read it as a teenager I thought he made the wrong choice, but as I grew older, took on more responsibilities, I began to understand his decision.
Cedar Waxwing's 365 
I’d never read that one, but it affected me even more than Gerald Stern’s roadkill poem.
Holy crap. I googled “Gerald Stern roadkill” and the third result was your blog post about the poem you referenced.
Wow. I remember seeing so many deer on the road, and the occasional dead one, when we drove around the states surrounding DC. Something we never see here. (Instead, they are in fields, farmed.)
Roadkill makes me sad.