If she’s not spayed, there is a very high chance that she will find a way outdoors, and pregnancy is very draining on their bodies. They generally have quite a few kittens because so many of them don’t survive. My most recent foster momma came to me practically skin & bones, and we lost 2 out of 5 kittens. Kittens are super fragile, and you can do everything right, but still lose them. And if they do survive, the shelters are already overflowing with homeless cats, so many get euthanized purely due to lack of space.
That’s actually something that varies from country to country.
https://www.thepunctuationguide.com/british-versus-american-style.html