I don't mean to scare you but I always thought that blood was a sign of miscarriage. I have no idea really. But the sites I checked said nothing about blood being a sign of labor.
 
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Your cat is due to go into labour around the 64th day of her pregnancy, although it is very unlikely that you will be able to be that accurate in your calculations. Instead, you will have to rely on your ability to read the signs of the stages of pregnancy and of her impending labour.
Firstly, you are likely to have noticed that your cat's appetite will have almost doubled in the past few weeks and you will be able to see her kittens moving around in her abdomen quite clearly.
Also, she will have been displaying nesting behaviour -- looking for a safe, warm and quiet place in which to give birth. Hopefully, you will have already provided a suitable nesting box for her to use, otherwise you may find that she has chosen to give birth in the middle of your bed!
Then, as your cat nears the start of her labour, her appetite will reduce dramatically. It may even disappear completely.
A further sign of your cat's labour is that she may become particularly clingy and want to be around you constantly, seeking your affection.
As she gets closer to the time that her labour begins in earnest, you may find that your cat starts pacing about, appearing nervous or particularly excitable.
Another very distinct sign that your cat is very close to going into labour is that she will begin to 'call' to you. Even if you have never been present when a cat is giving birth, you won't be able to mistake this particular sound!
As the time approaches, you will see your cat repeatedly licking her bottom as she reacts to changing sensations in her body as it prepares for the birth of her kittens.
And finally, when your soon--to--be mother cat starts to feel the first twinges of her labour, she will appear to be uneasy and will repeatedly go in and out of her nesting box, 'treading' on the nesting material that you have already provided.
When you see this last behaviour, you can be quite sure that your lovely cat is entering the first stage of the birth process -- your cat's labour has begun.