After a female cat is over six months old, she begins to enter the so-called sexual maturity stage. Female cats will continue to be in heat every 2 to 3 weeks from spring to early fall, making them easier to breed. Cats have an average litter of 3-4 kittens, and the gestation period is about 63 to 65 days, but if it exceeds 67 days, please seek veterinary advice immediately.