If you stress the fish enough she will abort a drop yes, but its not recomended and if she is not far enough along in the pregnancy you will end up with a load of undeveloped fry in wich she will just eat them up and recycle the eggs
hmmm ok well now i am going to ask the most ridiculous question ever, how do i tell when shes near? i know the gravid patch should be dark and big but should it be nearly touching her.. um... drop hatch, i have 2 that have big gravid patches and are sqaureish and round but i just dont know when they are ready
if they have become square try them in the trap overnight squareness is platys is definately a good sign but leave the light off as this helps not to stree them out too much
If you are watching them in the tank look for them behavior such as hiding in plants, hovering at the bottom of the tank, fending off other fish who come to close. Also, body movements like thrashing from side to side is a sign they ARE having the babies. If you see this and feel so inclined to move them, do so CAREFULLY! They won't die if you're gentle. I've moved my guppies when I see them having babies and they do just fine. Good luck!