The first thing is they will probably have a poor appetite.
Second, They are going to hide from all noise and find a soft place to get comfy and give birth. Third, They probably will not let you pick them up! Fourth, Stay your distance while the cat is in labor and still birthing. They usually will not make any noises to indicate labor!!!

 I had a litter of six with Goldilocks in 1995. If I would have taken the vets' secretaries' advices for the event there would have been some really bad consequences. So I was coached by experienced cat birthers instead. When a cat is nearing labor she will whail like the dickens you won't be able to shut her up. She will walk back and forth between rooms like she can't figure out what to do with herself. The more agitated she becomes the closer she will be. DON'T LEAVE HER ALONE! You have to monitor so that in case of complications you could help her. In my case with Goldilocks there were several. 1) she was young and did not have the instinct kick in so I had to bring the first baby to her and show her how to handle it. 2) her last kitten was breach. All in all, five of the six were born into my hand. But the first one was abandoned until I gave her to the mom.