What kind of render are you talking about ... Software, hardware? maya, Mentalray ? from the maya GUI, from command line ?
You may have to precise a bit what you're doing because, as it is, it doesn't make any sense !
At least for everything except maybe hardware rendering, the viewport size has nothing to do with the render.
You're not talking about "rendering" animation using the "playbast" function, I hope...
Guyb.