Ive been through that 3 times! They know when the baby is coming better than you do!! I didn't even know I was in labor but my kitty sure did. They very very smart like that. Everytime I was about to deliver my cat would rub all over my belly and meow at me rub against my leg and just generally be very cuddly!
All of my pregnant friends said that before they even knew they were pregnant, their dogs were all of a sudden extra protective of them and clingy/affectionate. It wouldn't surprise me one bit if cats were the same way right before labor.