A female cat (or kitten) will first come into season (heat) as early as four month old. She can become pregnant with the first mating. A cat’s gestation normally takes 58–65 days, we can say around nine weeks (you can remember it by comparing months pregnancy for humans). Siamese cats may carry their kittens for 71 days.
There are some signs to tell if a cat is pregnant (bear in mind: not all signs apply to all cats):
1. Enlarged and reddened nipples

About 15-18 days into the pregnancy, a queen’s nipples will “pink up,” or become red and enlarged. Her breasts may enlarge, and she may express a milky fluid.
2. Increased Affection

She may become more affectionate than normal and frequently seek out your attention. By all means, give it to her! My dear Lotto was always seeking for petting during her pregnancy. She was extra warm-hearted and full of love. She usually slept on my desk while I am working on the computer, and was using my arm as a pillow.
3. Increase in appetite
A pregnant cat starts eating more (I mean MORE). Even before the start of weight gain, her appetite increases significantly.
4. Weight gain in “burro” shape

She starts gaining weight, but not on every parts of her body. Because this weight gain has nothing to do with her increased appetite. Just the babies are getting bigger every day. From the side, pregnant cats frequently look somewhat swaybacked, with a slightly round and bulging abdomen. Many female cats assume this burro shape later in pregnancy. If she is gaining weight including her neck and legs, and not just in her abdomen, she may be just eating too much.
5. You can feel the babies kicking

During the advanced stages of pregnancy, you can feel the babies with your hand! If your cat is OK with it, you can touch her tummy and feel the babies moving, kicking, etc! My dear Lotto was allowing me to put my hand on her tummy. Feeling the babies was an amazing and unforgettable experience.
6. “Nesting” Activities
A few days before she’ll give birth, your cat will begin showing nesting behaviors as she prepares for the arrival of her litter. She especially looks for calm, a bit dark and isolated places like a closet, under the bed, etc. The place which she chose may not suit you, so give her a few suitable alternatives. I’ll mention about this more in upcoming posts later.
Avoid getting vaccinations, deworming, or giving medications to your cat if she’s pregnant. Consult your vet if any urgent medical care is necessary.
Sources
- “How to Tell if a Cat is Pregnant” on wikihow.com
- Signs a Cat is Pregnant on cats.about.com