(Perth, Western Australia, Australia)
I had a female Siamese come to me about 3-4 weeks ago. She was on call and mated with my male Siamese. I thought she was pregnant as nipples were a little larger and pinker and she’s a little fatter than before. But last night and several times today my male has been mating with her again. Can males mate with pregnant cats or does that mean she wasn’t pregnant from before?
Theoretically, a female cat can remain in heat for up to 21 days. She can mate with more than one male during that period of time and can have a litter of kittens which contains kittens from one male AND kittens from the other male. However, most often, if a female cat mates and is pregnant, she is not going to still be in heat up to 21 days later. Your female would had to have been in heat after conceiving with your male cat if she were to mate with him again. That is highly unlikely.
If the cats mated initially several weeks ago, your new female was likely not pregnant from that first interaction. Females are only receptive to mating when they are in heat. There can be false pregnancies in cats, so you may very well have been seeing the symptoms of pregnancy without her actually being pregnant.
There are also pregnant cats that have miscarriages so she could have been pregnant but lost the kittens.
Please visit Pregnant Cat Symptoms to learn more about pregnancy in cats and to read submissions from other cat lovers.
If she isn't pregnant, I would strongly urge you to have her spayed. She is much more likely to develop mammary cancer or a uterine infection or uterine cancer if she is not spayed. There are also so many kittens and cats in the world that need homes, I personally feel it is a shame to let a cat have kittens.