What happens next?

How to take care of baby platy fish
Be on the lookout for pregnant fish.
Pregnant platies are easy to spot, so if you keep a close eye on your fish, they shouldn't be a surprise. A pregnant platy will develop a noticeably swollen belly.
It's also common for a pregnant female to develop a dark spot near her back fin. This is caused by the eyes of the unborn fry pressing against her scales.