Hi,
At about 21 days after mating, they do what is known as 'pink-up', which means that the nipples will become slightly swollen, and pinkish red at the bases. From around five weeks of pregnancy, you will see the gentle swelling, which then obviously gets bigger. A few days before they are going to have them, you will be able to feel the glands around the nipples filling out with milk. Kittens generally arrive between 63-65 days, but can actually be anything from 59-70 days.