HI,
I am a GC holder and my wife's GC is in process through marriage based GC. She is currently in USA with me.

Can we sponser my wife's parents to come here to USA on tourist visa while her GC is still in process?

if there is medical reason ( your wife is Pregnant ) then you are 100% good to go. But still you can try, i have seen some people's parents been here even they don't have GC !

instragram, would that be a good reason to sponser them? Dont embassy usually deny if its because of daughters pregnancy? what are the chances of approval even if my wife's GC is till pending and she is pregnant. My wife currently holds a student visa

If she is having baby its sure they will get visa. i have seen Pending asylee's parents been here for that reason. Your wife has better status.
Other reason will be visit only which has very less chances of getting approval , but highly depends on your sasu saruras status in Nepal (income , work , bank balance) .

thanks for info

I have seen several ppl coming here cuz their daughters or in laws R pregnant..you'll have higher chance of getting visa based on this situation