Kiểm tra núm vú. Quan sát đặc điểm hình dạng “con lừa”. Quan sát hành động chuẩn bị ổ.

I'm interested in that, but I only have a few mins. Can you give me at most the first 500 characters of a detailed explanation in English about that?
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. Enlarged nipples are also signs of being in heat, so bear in mind that growing nipples are not exclusively indicative of pregnancy. 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 your cat is merely overweight, she