The max that is able to be spawned is 38...I need some more testing to confirm but as far as I can tell it is not possible or needs extreme precision.
Update: I am unsure if killing the babies as soon as they spawn will make the motherships spawn them faster but it may. I will be trying that out and let you guys know as soon as I can--however my game data for the game just got corrupted in the middle of it so that's always fun...