I dont' even have a male platy and mine can't stop giving birth.
Your females are more than likely pregnant already anyway. If you want fry to survive, because you most likely won't see a platy giving birth if you are not experienced, make sure you have enough plants for them to hide. You also won't see the small platies for at least a week after they are born, as they are just so good at hiding it's unbelieveable.