Welcome to TCS. There are very few signs to predict when a cat will give birth. Do you remember how long ago you first saw the kittens moving? She should give birth 2 - 3 weeks later.
Within 24 - 48 hours she will lose her mucus plug and her water will break. She will be uncomfortable, affectionate and she may have soft stools/diarrhea.
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[article="31496"]How Do I Know When My Cat Will Give Birth[/article]