What to do if your cat is expecting kittens?
What is the problem with leaving your puss at home every night if she’s expecting kittens? Well, as an experienced kitty savior I can tell you that you, as her human, can do an estimate calculation on when will the kittens be due, but at best it is only an estimate. She can begin labor at any time and at any location; as a responsible owner you certainly do not want that, especially since her having her kittens outside your home will also mean that she will stay out for the remaining of their childhood.
Giving birth anywhere means also that her kittens, as well as she, are exposed to all sort of predators - and that includes the neighborhood children who can misbehave when they are outside their own homes. If her kittens and she are lucky, then she will give birth to them at a home where they will be cared for, but, as with any other street bound cat, she will be taken to the local shelter and put up for adoption. That means that you will never see her again.
What to do? Keep her inside. It is hard, but in the long run, you do not want to miss her becoming a mother and being first witness to the wonders of birth, do you?