If a female cat isn't spayed, then her heat cycle is just an inevitable fact of life. When a cat is in the midst of her "mating season," she'll likely make it known to everyone, whether through incessant nighttime vocalization or persistent attempts to escape your home. Look out, world!
Pregnancy
An increase in a cat's nipple size usually indicates pregnancy rather than the heat cycle. Not only do the nipples tend to get bigger during pregnancy, they often take on a bright crimson appearance, too. If a cat's nipples have a rather "swollen" look, that also could be a sign of pregnancy. This development usually appears around the third week of a feline gestation period, which usually lasts for a little over two months.
Other Signs of Heat
Larger nipples usually aren't a sign of heat, but there are plenty of other indications to go around. Some telling signs that a cat is in the middle of heat include uncharacteristic loving behavior, restlessness, positioning the body in a "mating" style, excessive yowling and meowing, irritable behavior, attempts to run away and urine spraying.
Other Signs of Pregnancy
In unfixed kitties, bigger nipples usually mean "gestation time." Hello, future kittens! However, if you need more clues as to the state of your pet's womb, be on the lookout for other key signs of pregnancy. These signs include low energy, increased desire for attention, appetite swings, throwing up, nesting behaviors and -- no surprise here -- a conspicuously protruding lower belly -- aww.
Spaying
If the idea of your sweet cat going into heat or getting pregnant fills you with worry and dread, make it easier on yourself -- and your precious kitty -- by getting her spayed. Not only will spaying entirely eliminate the concept of pregnancy, it will also stop your little one from having to deal with the frustration and restlessness of the heat cycle every three weeks or so. Not to mention, fixing a queen cat inhibits various very dangerous ailments, including breast cancer and uterine infection.
Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.