I keep my preggo guppies in flower vases around my office. Some people like flowers I have fish. lol I wait till I think there gonna pop then I toss them in a vase filled with
Java Moss and gravel or sand, let them drop then return them the main tank and add fry to my fry tank. For the most part I'm starting to get good at it I can usually tell within 3 days. After I've moved fry and momma I do a 100% water change on my vase and add the next female. It's working really well I've probably got 10-15 females and 2 vases.
I cull pretty heavy, here latley I've been getting crooked spins and weird tales form a good line I just bought they go straight to my big fish tank for a snack.
The other thing you could do is make or buy a divider. I usually keep my guppies in a fry tank for 1 month at that size they can't eat each other, at one month they go back to a main tank, they are still small but fast enough to get away from the adults.
I'll have to take some pics of the maternity ward.