I googled laparoscopic spay, and it seems that this is common surgery now rather than using an open surgery.
Incisions in laparoscopic surgery are much smaller than otherwise, as there just has to be slots for narrow tools and a bigger one to get the organ itself out. For example, an old gallbladder removal for a person required about a five-inch or so incision, and now they get away with a couple of half-inch ones and a couple of one-inch ones. At least that's what I had. I bet a cat's uterus is smaller than a gall bladder, as long as it has no kittens inside.
Actually, it's probably way smaller. I watched a laparoscopic gall bladder removal on youtube before, and now I have just watched a spay of a pomeranian, and comparing the organ to finger size, the uterus is much smaller, so would require a very small incision to get out if done laparoscopically.